Getting older variants of each aircraft isn't realistically going to happen, but giving mission makers these options feels like a relatively simple option that would enhance experience greatly.
You can already disable JHMCS but can not stop players from requesting ground crew to put it back on.
As for datalinks, a ghetto solution could be just simply making the switch that turns them on not functional, ideally based on mission date even.
The F-16 we have and F-15 we are getting are not radically different from the 80's variants, so the ability to limit JHMCS/DL in combination with weapons restrictions can provide a close enough experience to the planes that would have actually been there in the 80's.