Bethesda will never drop Gamebryo/Creation sadly. Starfield and TES6 are confirmed on Creation, and I have no doubt that early development has already started on the next Fallout game.

I can only hope that they borrow id guys for more than just the shooter mechanics in the next one.

It's a weird id world anyhow with Rage 2 using the Apex engine. Gameplay footage looks very idTech like so far, to me anyway, with look and feel. The collaboration seems to be benefiting both teams. Apex with some id tweaks might be a solid path for the FO series. Although, I was hoping to see how far the idTech engine could be pushed for open-world design. Maybe the collaboration pulls some ideas into the idTech engine.

There are a lot of hints in RAGE and the Wolf games so far that indicate in some ways they were testing how well Fallout aesthetics would carry over into the idTech engine.

I have a hunch that if RAGE had turned out differently, we would have seen a Fallout game on idTech by now.

I think it's still possible too - there are some environments in Wolf 2 (you'll know them when you get to them) that still look like an audition for the role.