Honestly, I wouldn't like Obsidian working on a new Elder Scrolls game, simply because it's Bethesda's series, while Fallout is the baby of many of Obsidians designers.
That being said however, I am tired of people calling Obsidian a horrible developer, yes they need a much, MUCH, stronger QA team, yet they have the capability to create amazing games, they have solid story, multi-dimensional characters and factions, with flaws and strengths. Their stories have depth symbolism and humor that is better than some books I've read. I believe that they are best suited to develop the Fallout series better than Bethesda is, FONV's story and companions were better, with a similar gameplay style to FO3.
I'm not forgetting Obsidian's bad points (buggy gameplay in FONV, horrible ending in NWN2OC, etc.) but their good points definately outweigh the bad, FONV's storyline and DLC was amazing. In NWN2 the overarcing story, the trial, the keep minigame, the companions, it's first expansion are all spectacularly done. Alpha Protocol's dialogue system is impressive.
Obsidian is hit and miss for a lot of people, I realize that, some people like playing for gameplay and fun and don't pay a lot of attention to story, while for some it is the exact opposite. It's just like how some people enjoy Twilight while others prefer A Song of Ice and Fire.
All in all, I am hopeful for the Wheel of Time game that they're creating and I really hope it turns out well, but they should stay out of TES except as maybe advisors to the creation of the storyline of the game.
Edit: Anytime I see preference to Fallout 3 to Fallout: New Vegas, I don't see a lot of reasons of why they enjoyed that. If someone would post why it would be appreciated. Please don't say story, the story of Fallout 3 has a plot-breaking flaw that could be seen by anyone with grade 11 chemistry or physics.