Honestly I'd like to see Obsidian do a turn based RPG like Wasteland 2, Divinity Original Sin, or even like the original Fallout 1 and 2.
While i absolutely loved Pillars of eternity, I am not a fan of Real time with pause in general, at least not when you're dealing with big parties (it's more managable in games like Knights of the old republic or dragon age, then it is for a full party in Bauldurs gate or Pillars, in my personal opinion).
If they did get a run at fallout again, I'd actually like to see obsidian make an isometric turn based version, given a bigger timeline than they did for new vegas and set it wherever they wanted really, but with the budget backing from Bethesda.
Or something i'd also really like to see, if Obsidian was allowed to make an isometric turn based (just like the original fallouts) of an Elder scrolls 'side' game, set wherever and whenever they wanted.