I would love a future era going into sci-fi-ish territory, but probably not likely.
The more info we have about modern civs, the more probable it looks for one of the future expansions to add 4th era. All modern civs announced so far ceased to exist in 1870-1950 period and names like Qing China or Meiji Japan suppose there is more modern (contemporary?) age for those civs. The choice of Buganda as modern civ also implies Firaxis wanted modern age civs which didn't survive by now.
Take in account they always tend to leave the end of tech tree for later. So we don't really know how far it goes. If there is one hint would be Ed saying before the game goes up to the division of the atom, albeit that could just be a generic comment not wanting to spoil what the end of the tech tree will look like. Also global warming should be in, which indicates the tech going further than just 1950-ish
Regarding the civs, I think it is more likely they trying to avoid representations of actual current nations as people can easily be very sensitive about it, just like how they avoid leaders that are current alive people or recent controversial ones. For previous games it didn't matter much because the civs were supposed to represent the nation whole history, but now that they're representing a moment in their history, I can see they trying to avoid very current representations. To the point where, if we ever get a future age, I would expect more likely a generic representation or completely invented ones, maybe inspired by sci-fi novels and the like.
Insufficient data at present to form a clear hypothesis.
Pretty much, yeah.
I would say that there are neat gaps for Medieval-Industrial-Future to fit into the future of the series
I think it is extremely unlikely for them to add ages in the middle, as it would need a completely rebalance of the game. Too much for even an expansion.
On the other hand, a future age could be released on a separated big DLC for it, where people who are not interested could just not buy it and continue to buy other dlcs that would work normally up to modern age, and even those who buy it, it would be easy to add an option on new game to make it end on the modern age for when someone with it want a shorter game.
I hope there’s not a fourth age myself. Just focus on expanding the three we have. Future was by far the most boring part of VI anyway.
I think part of that is the result of the problems like snowballing and how even if you get there you already would clearly know if you can win or not, so it would often feel like just passing the turns to finish doing what you need to win. But that is exactly what the age system is made to avoid, so if implemented well, it could be as fun as any other age.