Age of Sci-Fi , the only feasible and logical next RTS for the series?
A big question is, what can be next for the series?
The Age games so far do cover history from the Stone Age to Napoleon.
More modern history and near future would not fit the gameplay.
We kind of have a game on the way as a spiritual successor for Empire Earth that did it,
so its kind of covered too. Not to mention that other games and gameplay do better handle this time periods.
For fantasy we kind of have Age of Mythology and Rise of Legends. This setting is also very good covered with other games.
So the only thing left, it seems something like a mix of Starcraft and Starwars Battlegrounds.
Sci-Fi is kind of more creative and more feasible for DLCs and additional content to pay.
We could start with something like Resistance from Terminator, than go over to people who ride mechanical animals from Horizon Zero Dawn and add some kind “mad max/water world” faction. You can have here a lot of creativity.
an age of spinoff set in sci-fi setting would be an interesting concept, there’s just 1 problem
age games so far all had very logical to learn unit roles provided by real historical material, that includes aom which used depictions of mythology with few creative liberties to make gameplay around
i don’t have a clue how one would do that with sci-fi setting as cleanly as other games have
good idea, maybe list first all the problems that could happen and than think how to solve them.
-Next issue is, Age of Empires games are kind of melee /close combat games.
that just would work bad with realistic long ranged units.
-Another issue, would be to make a proper base build game around it.
As to work in terms of gameplay people like,
the game would need a base build concept that is more complex, but still handy to use.
-space combat was always for those games an issue.
more ideas , what could be an issue?
this way it would be easier to write in first post a suggestion or solution for it
Someone beat you to that idea two years ago 
:
Terminator: Dark Fate - Defiance en Steam
the game should be in direction of Age of Empires, a Terminator and Warhammer 40K game is kind of too grim dark and lacks base build. People who pick the game up, should feel at home from first moment on and be not too alienated. Maybe use the sheep as the mascot?
so no matter what biome you have, the sheep is the familiar anchor and gameplay element.
