Just objectively speaking - the best options are:
Postcolonial:
Mexico/Peru/Argentina/Cuba in descending order
Pakistan/Bangladesh
Vietnam (I think presenting them as a modern civ would be a decent option)
Philippines
Myanmar
Precolonial:
Tibet or Himalayans
Swahili
Kongo
Europeans(clearly lowest priority):
Italy
Hungary
Bohemia
Ukraine
Belgium?
Just objectively speaking - most of those options peaked at times other than you've listed them for.
Mexico/Peru/Argentina/Cuba are all well and good, but they don't stand out in modern times as world leaders in anything, nor have they in their history. Most of them are quite unstable politically or economically too. There are however plenty of good options for pre-colombian civs from the Americas. South America sitll has just one....
Pakistan/Bangladesh in the world since their formation have had economic growth and a population boom, and been a little more unstable than the country that's in and already covering those bases: India. India is by far and away the worse representation of an areas history i have ever seen in this game, so to waste another opportunity to bring in a civ like the Harrapans or the Mughals or the Mauryas would just be tragic.
Vietnam as a modern civ, hmm. Well at the moment it's a jolly nice country but it's not exactly been renowned in the world for anything other than the Vietnam war. The war that's only really significant as part of the cold war, and america and russia's history. To Vietnam that wasn't a great time, and certainly not the best time in its history. Vietnam has had a much better time in the past, and i'd love to see a Hindu Vietnam in game myself as the Champa.
I have no idea why you'd want to see a modern philippines. Again that has links to colonialism through america and spain and will inevitably be a disappointment. I don't know anything about the pre-colonial history of the philippines but i'm sure they've got buckets of it.
Myanmar has been mentioned above me, but this would just be the worst precedent for civs to be added if it's modern form gets in....
Belgium is a completely artificial country that is a combination of the dutch and french civilizations. It was designed as a buffer to french aggression (essentially a puppet state), so i don't know why it has a place in the franchise. We'd be better off with the european union... But only narrowly.
As for the rest, i can agree enough with them, except that they are objectively the best options. There are plenty of other good'uns out there.
(P.S. i believe you may have meant subjectively

)
Australian/Canadian civs would be brilliant. Both have native peoples and cultures that can be used in their Unique Attributes (and can potentially cover huge swaths of time like America, Ethiopia, Japan, Russia, Germany, Denmark, Arabia, Brazil and Poland). Both the Inuits and the Aboriginals can offer a proverbial myriad of attributes to a potential AUS/CAN DLC in the way of abilities, units or even buildings.
In regards to Australia/Canada, their cultures, peoples, geography and unique traits give them as much in common with Britain as Brazil has in common with the Portuguese. Not a hell of a lot. All three were colonial nations and have made their mark on the world by being unique.
Why don't we have an Israeli civ based on a Palestinian UA while we're at it?

To call Australia now the same civilization that is was when it was populated by aboriginals is just absurd :S You've either gotta have one or the other in my book. There is literally no way an amalgam civ of that sort can be called a civ. What would you think if America covered all the native americans with part of their UA? I just can't even begin to describe how wrong that would be, historically and in terms of political correctness (dare i use such a phrase...)
As for the being similar to Brazil-Portugal, that's just plain wrong. Brazil has existed as an entity for over 500 years. Australia just over 200 years and Canada around 500 years too. However, brazil has also been independent for very nearly 200 years. Aus just over 60 years, Canada just over 70. Additionally, Brazil as a post colonial entity is a highly multicultural place with larger links to africa than to europe and strong links to its pre-colombian past still remain too. Australia and Canada and highly Europeanised still. They are very much majority white and majority british decendants, with Canada throwing in some french too. Neither one of these countries is far distant from the UK, and Canada has grown closer to the USA, but it's still a generic western country, while australia is basically britain with funny accents - till the 1970's they almost exclusively took british migrants and they have a similar kind of relationship to the uk as england, wales. northern ireland and scotland have with one another.
I'm not saying they are not unique as post colonial entities, everywhere is unique. But they haven't diversified a great deal yet. I wouldn't mind them being in eventually, but to me it is sacrilege that they be added before dome genuinely different, unique and successful cultures from elsewhere and other times.