Warning: Long Post
Since Brazil is an official Civ VI civilization, it seems more likely that Australia might be considered - at least with later DLC, so I hope there is still time to influence Firaxis so that it might be an optimal inclusion.
I've reviewed the specs of the Australia Civilization mod for Civ V, and I feel it could be improved.
Firstly, it features several unique buildings, one of which is the Refugee Programme!? Is this a joke? Refugee Detention Centre would be a much more appropriate. The modern era building is the Tourism Department, which is just too generic, but definitely headed in the right direction.
The unique Australian building I would suggest would be associated with the surf life saving movement, which was first established in 1907 - a world first. It could be represented with the beach watchtower, or beach clubhouse. It would obviously give some kind of tourism or happiness bonus.
This is a more appropriate choice than Tourism Department, as it is strongly associated with the Australian beach and tourist culture.
Edit: Actually the R.S.L Club/Leagues Club might also be an appropriate unique building, giving an economic bonus.
As for the leader, I think Edmund Barton is more suitable than Henry Parkes. For one thing he was the first national leader. But for a less venerable, and more iconic and colourful leader, you couldn't go past Billy Hughes.
The unique military unit I think should be the Light Horse. For once thing, it was an official army regiment. Diggers on the other hand were not unique to Australia, were not an official regiment but just a slang term given to infantry, and were not as prestigious as the Light Horse.
I think Australia should be included at some point officially, but definitely needs a bit of research on the part of Firaxis.
Author of the original Australian civ mod here (or at least, the one you're referring to). The mod you are referencing is seriously old WIP version of the mod on this website that I probably should've deleted long, long ago. Nevertheless the current version of our Civ mod is pretty damn different to when it started out. You can see
the current UA design as it stands is completely different from when it was released a few years ago:
Boundless Plains to Share: Settlers found

Puppeted cities that generate +1

Tourism. +1

Tourism for each outgoing

Naval Trade Route. Cities that generate +2

Tourism or more expand

Cultural Borders twice as fast.
We also still have the Prime Minister and the Digger as a the unique civ picks. I can understand why they in particular might seem like lazy attribute choices, but they were actually concious design choices. Our aim isn't actually really to 100% replicate a Firaxis made civ, which tend to be more on the bland and flavourless side. In general, what we do is inject our mods with really high dosages of flavour somewhat to prove that these civs are worthy of being looked at. In a sense Civ allows for a pretty decent platform to serve as a quasi-educational tool to highlight unique peoples, struggles, stories, civilizations and cultures not dictated by what's taught in standardized history textbooks.
With Aus, the job was to make them full of flavour by including Henry Parkes as an unconventional choice. That way we can essentially tell the story of Australia's founding and eventual federation. Founding the colonies, and then annexing them later on when mutual cooperation is beneficial is supposed to be akin to federating the separate colonies. Barton almost seems like the logical choice, and I'm also somewhat biased towards Barton because we're apparently related - but I think I'd prefer Curtin or Deakin if not for Parkes. The Digger was a pick to represent the Boer War-WW1 era soldiers, but I agree - I think we are due for a change. I like the idea of the CAC Boomerang or the Light Horse.
With regards to the leader choice, Parkes wasn't the leader of Australia, but he was the leader of the colony of NSW for over six terms. The mod is intended to replicate founding the different colonies of Australia, then uniting them in federation. This is also why we made Sydney the Capital, since it's the oldest, first and one of the most important historical cities in Australia, but also the Capital of NSW (where Parkes is starting is to convince others to federate over time). Canberra would probably be our capital if we're going for a leader like Curtin
(which is what we did for the specifically WW2 Australia mod).
In regards to Canberra also, if you have Events and Decisions installed, there is this unique decision:
Resolve the Capital Dispute Edit
Our two great cities, Sydney and Melbourne, have been at loggerheads as to which should be the national capital since the process of federation began. Such madness cannot be allowed to continue if we are to remain unified as a nation. Perhaps a different solution is called for…
Requirements/Restrictions:
- Player must be Australia
- Must have founded four Cities
- All Australian cities must be annexed
- May only be enacted once per game
Costs:
- 500

Culture
- 1000

Gold
- 2 Magistrates
Rewards:
- The fourth city founded by Australia becomes the Capital Capital
- A Prime Minister appears in the new Capital Capital
- A

Golden Age begins
- Cultural

Great People generation rate increased by 25%
We also picked the Prime Ministers (which have the ability upon appearing - cayses all non-puppeted coastal cities to yield +1 Tourism Tourism per owned land tile outside workable limits) as a Unique to represent and showcase the endearing legacy of Parkes' work. If we were given the task however to blueprint official Civ V DLC for Australia... then we definitely would tone down the flavour and leave most to the Civilopedia. However Civ VI presents us with the opportunity to really expand, because it allows us to import lots of flavour without trying too hard

.
Since Civ VI is also going for characters, Parkes is imo definitely the best choice. Parkes was such an interesting distinctive
(dat beard) colonial character, he started out as a penniless uneducated immigrant, made a career for himself, wrote bad poetry, and eventually became the most commanding figure in Australian politics. As a leader he was this massive blend of egotism, vanity and deep egalitarianism.... which to be honest lol I think represents more Australians than not. Being able to represent that sort of idealistic uniquely Australian character with a well done accent (and beard) in Civ VI sounds like a pretty exciting project for Colonialist Legacies in the future.
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I'll post bellow our current design plan for Australia in Civ VI if modding allows for it. We're cautiously optimistic, but it helps to be ready to work on something in the mean time and the entire design process is pretty fun. It'd be good to have some more eyes and feedback on what we should include or trim down in terms of balance and design. Also for that reason, I included a few more mechanics than usual to see what is preferred and what should be trimmed. Everything is subject to change at this point.
Civilization VI - The Australian Commonwealth
UA Name: Boundless Plains to Share
UA Trait: 
Border Growth increased in Cities further away from the Capital.

Trade Route length limitations ignored when sending Internal Trade Routes to Cities on the same continent.
Leader: Henry Parkes
Leader UA: Gain +5%

Tourism output from each Natural Wonder tile if the City containing them is connected to the

Capital. First City founded in the Modern Era is founded with additional Population and becomes the

Capital.
Leader Agenda Name: Mateship and Camaraderie
Leader Agenda Trait: Loyal and friendly to frequent trade partners. Will often follow friends with larger armies into wars.
Unique Unit: Digger - Fights more effectively overseas, and has the ability to construct roads. Replaces the Great War Infantry.
alt. Kokoda Trailman, Light Horse, Boomerang (CAC).
Unique Infrastructure: Gaol (building) - Has additional housing, and gains a

Food Growth bonus for every Foreign Trade Route sent to the City. Foreign Cities sending a Trade Route to a City containing a Gaol receive additional Amenities. Abilities (including housing) obsolete when entering the Modern Era, at which point the building generates Tourism.
alt. CSIRO Lab, Station (as in Outback Stations), Colonial Parliament
At this point I'm trying to decide whether or not to head down as flavourful storied a route for as we did in Civ V, to make it somewhat more approachable and accessible.
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Also guys, please never make mods that combine Indigenous Aboriginal Cultures with an Australian Culture... things get reductionist super quickly. Individual Aboriginal peoples deserve civ representation in their own right.
