Sorry, didn't mean it as an attack...

Wanted to make a stupid joke, I think it came off as a bit aggressive...
But yeah - the Sistine Chapel is not in as a wonder because its ceiling is in as a work of art. That has been confirmed, so no need to search for a different solution to this problem.
Since there also seemed to be a lack of late game units, and nothing after the Medieval/Renaissance Era should even be of our knowledge, it wouldn't surprise me if there's units/buildings/wonders not yet assigned a tech. From my understanding, it's the units and buildings that are assigned techs, and not the other way around, so the tech tree could very well be finished, but not the units and buildings.
Either way, if not right now, then I'm sure they'll add all of those wonders in DLC or expansions!