Not saying I would never play Oblivion again... but I don't see myself a lot of reason to once this comes out. The only reason to go back would be to play new mods, or just to experience a particular storyline again, especially one that might be relevant in Skyrim. Other than that, I'll be sticking to Skyrim.

I hope it will be good enough to prevent from playing Oblivion. But I will probably still play Oblivion because I like Cyrodil.

After i finish Skyrim i will start on Arena and Daggerfall.

I thought Morrowind was infinitely a better game than Oblivion.
I think Skyrim will be better than both combined, though.
It looks to me like Bethesda took the amazing stuff from Morrowind, and the few things that Oblivion improved on, and made the best game so far.