I don't think one can say "it will be a problem" because there are so many different ways to do a game (do you really think "terrain tools" matter in something like Terraria???!), all one can say is that "it might be a problem", which is what I'm saying, and judging from my experience with it it will be more of a problem for people doing 3D worlds with terrain, pathing and so on than for people doing 2D or, like me using 3D as a sort of moving gallery to show in a nice way what would otherwise be pretty bland.

Whilst I'm currently on vacations, next week I'll have to start evaluating both Godot and Unreal for my project - which, as I said, whilst it does show things in a 3D view, is architectured so that the game essentially runs in data space with user-input coming from the framework (and it's pretty easy to change that because it's centralized) and on the other side the framework rendering visual views of the data.

My plans to upgrate to the latest Unity are now shelved and I've already planned how I'll remove the last pieces of Unity influence (basically Vector2) from my data layer and make sure it's totally separate.