If the argument is that Venice as a CS has been replaced by Riga, surely that is more likely to imply a Venetian civ rather than an Italian civ?
In the absence of other information that can't apply equally to Venice or Italy, it's impossible to say. It's rather unlikely that they'd make an "Italy" civ which excludes Venice, and even more unlikely that they'd make a Venetian civ which excludes Venice.
He was a great leader for the Carthaginian military. He was a mediocre leader of the Carthaginian state. He deserves to be a Great General, but he's not a great choice as the leader of the civ.
He is a Great General (as Gustavus Adolphus still is despite now also being a civ leader...)
I don't think its a given, that a Native American civ is in at all. As others have said, the Pueblo might have been planned as their one Native American civ (Since they were a perfect fit for Brave New World). Its possible we see no Native American civ either and end up with another civ we don't expect
The Pueblo are irrelevant. We don't know whether they were the only civ planned that didn't make it in (the wording that introduced the Pueblo story at PAX suggested they weren't) and we don't know whether Firaxis tends to replace "like with like" when circumstances force it to reject civs. Despite popular opinion, the Pueblo don't have anything to say about whether or not there will be a Native American civ.
Much more compelling is the fact that a tomahawk-wielding unit with a mohawk exists in the code, and has been seen in the main game rather than a scenario. This is better evidence for a Native American civ of some kind - particularly eastern Native American - that exists for Italy or Venice, for which we have a very plausible scenario that a city-state has been replaced with one or the other civ, but no sightings of any uniques that might give away that unit.
Of the available options, the Sioux have been in the game before and likely meet the requirement for being one of the 'fan favourite' civs to a degree other options don't, and the likely leading alternative - Cherokee - is technically possible but is ruled out in generally favoured interpretations of the achievement list order (which posits either Italy or Indonesia as the 'missing' slot between Brazil and Morocco).
True, Indonesia still has a chance, but my point still stands. There are quite a few fans who have a favorite civ that's deserving, but is often short-changed for others. (Hungary, Kongo, Argentina, Armenia, Israel, etc.) For us, a third expansion would mean the chance for some of them to get in, and set a precedent that in civ 6 could mean that they would come earlier, and not as the last choices. 50+ civs is a lot, but world history is big and has had a lot of important civilizations. Personally, I wouldn't be unhappy with a DLC run with the civs listed, but they have already indicated that more DLCs are unlikely, so I'm hoping for a 3rd expansion a lot.
This may actually be a consideration - if they add all the favoured civs to Civ V, what new can they add that will sell Civ VI? In fairness Civ V hasn't been short of new 'fan fave' civs - Brazil, Poland, Assyria, Iroquois, and quite possibly Venice - and Polynesia was purportedly based on suggestions here. Getting rid of unrealistic and undeserving fan options like Inuit or Israel, politically contentious ones like Tibet, fan-contentious ones like Italy (if not in BNW) or simply unlikely ones like Australia or Canada (really, do you expect anyone could take a game seriously if, close to the top of its civ list, you have something like "William Bligh of the Australian Empire"? Particularly since Australia's other leader options would be either forgettable or silly - heaven forbid they go with Ned Kelly. A civ led by Slim Dusty would make as much sense...), the pool of civs that large numbers of fans really want is probably rather small. They have enough to lure people with Kongo and recently-popular Hungary, I suspect, but they may want to hold Indonesia back for similar reasons.