A Fallout alternative...
If your not familiar with Xenozoic Tales which later acquired the more catchy title Cadillacs and Dinosaurs it was one of the sources of inspiration for the original Fallout launching all the way back in 1986. It's rarely ever mentioned but I definitely read some acknowledgement somewhere long ago from someone who worked on Fallout, particularly the iconic Fallout artwork with a couple in blue jumpsuits was derived from Xenozoic Tales art.
Indeed Fallout shares shares a lot in common, both universes have a retro 50's look mixed with high tech and are set in a post apocalypse earth. In C&D's case though it's not because of Nuclear war rather some eco disaster but when humanity emerges from their vaults centuries later they find dinosaurs roaming the earth again.
C&D seems to have been largely forgotten but it achieved some popularity in the 90's even getting a cartoon series (only partial episodes) which is actually worth a look it covers many of the kind of stories you find in Fallout with lost tech etc. in one episode they even reanimate an android human from the past.
The author Mark Schultz is now in his 60's and I think he has retired so he might be open to someone like Obsidian have a play around in the universe.
No-one could accuse your of being a fallout clone with C&D obviously pre-dating Fallout by quite a margin and dinosaurs are super popular again thanks to the Arc Survival game.
However I don't think Obsidian could afford the budget for a full 3D Fallout 4 style game, maybe a Kickstarter with something like Pillars of Eternity, sell it as a retro Fallout, any interest Obsidian ???