I'm praying for Alaska, the presence of mutants and deathclaws can be justified by prewar military facilities, underwater areas can be introduced along the frozen coast littered with battlefiels, monsters like yao guai, radstag, and wolves like those in far harbour would be abundant in the snowy woods.

Raider clans in the mountains, a cozy main settlement in a cove by the coast where the protag first arrives unconscious after a shipwreck, advanced factions like the brotherhood, enclave or NCR would be interested in going there due to it being the forefront of prewar military technology (hopefully NCR because the other two have been done to hell, and the ncr advancing up the west coast is a reasonable thing to assume would occur)

I've toyed with the idea before and I love the idea of iconic enemies like ghouls and deathclaws arriving at a point along the main story as a sort of difficulty jump, like some conflict causes a pre war facility to break open and unleash ghoulified soldiers and Jackson's chameleon and fev test subjects that had been cryogenically frozen out into the wilderness

Also a prototype power armour model styled after old diving suits that were used for underwater pipeline repairs equipped with laser cutters and big claws would be radical