That's entirely possible. But let me share another thought I've had, as I've been mulling over this matter; it's half-baked, but maybe I can get it fully-baked by trying to put it into words.
So here's a form of historical unreality that exists in 1-6, and that I have just accepted as being in the nature of a Civ game: playing as the Romans, I can build the Pyramids. My in-game version of a particular civilization can build a wonder that the this-world version of that same civilization did not build.
To use my case from above, if I'm playing 7 as "America" (in that I plan to get America as my modern-era civ) why can't I similarly say that the particular incarnation of America present in this game had hoplites as its early unique unit? On the surface, it's no more unrealistic for America to have hoplites than for Rome to have the Pyramids. (and that's what we're trying to get at, why civ-switching feels unacceptably unrealistic whereas earlier violations of this-world history felt acceptably unrealistic).
But here's the problem with that analogy. In Civ 7, I'm not America at the time that I'm playing with hoplites; I'm Greece; everything about the game is telling me I'm Greece. Nothing about the game is telling me I'm America. There's no "bag" for the historically-unrealistic thing--American-hoplites--to go into, the way there is a bag for Roman-pyramids to go into.
These reflections have helped me to pre-envision how I think I will play civ 7 should I ever pick up. I think that I will name my civ after the thing that does remain stable throughout the game, the leader. So (in my headcanon) I will play as the Franklins or as the Aminites. Then it will be fine if that imaginary in-game civilization has hoplites during its antiquity phase and marines in its modern phase. It will even be fine that the Franklins had an early "Greek" phase of its civilization, followed by what historians refer to as its "Mongolian" phase and eventuating in the present "American" phase.