No I am just being realistic as an actual game developer. This is not a conceptual discussion. It doesn't make any sense to implement this change because if your fixed timestep for the physics system is breaking down then gravity not calculating correctly is the least of your problems. The controls would be unresponsive if the dt became large anyway. You are talking about more than doubling the number of operations for all acceleration based movement which is just about every movement and applied force in the game. If you thought the framerate was hurting before because too many objects were on screen doubling the physics calculations is not going to help you out. It might not hurt that bad but it really depends, you would need to profile it. It doesn't matter though because the tunneling would be another bigger issue that you would also have to address for this to even matter, and that would definitely hurt bad to check for.

During the far majority of use cases the timestep is fine, and you are just creating deadweight by doing this. Plus I guess you are now doing tunneling checks as well to create further deadweight for the rare occasion when someone has framerate issues.

I am looking at this in the sense that I would actually implement this in a game I make, and I would not because the upside of doing this is basically "if the game is already fucked I want it to be maybe not as fucked but still having many other big issues with pretty much every other component of the game logic", vs a bunch of deadweight when the game is running correctly, which should be 99.5% of use cases.

Am I adding assumptions here? I guess so but they are real ones for real game developers. Unless you are doing something very unusual these would be your concerns.

This is not an academic exercise for me like it maybe is for you and most of the commenters it seems like.