I doubt I'll be getting Skyrim now but, if I did, I don't think I would do anything special. I know I didn't do anything special in Morrowind when Oblivion came out. If I ever do get Skyrim it will not impact any of my Oblivion games or characters in any way. They will continue, unaffected, as though Skyrim had never happened.
It's a nice idea, though. I like it.
I agree. I play both Oblivion and Morrowind, and doubt I'll get Skyrim until the price drops, the mods are out for a year or more, I have a more powerful system, and friends I trust can report its as great as the pants-creaming kid reviewers for the major sites. That's quite a lot of conditionals.
Oblivion and Morrowind are almost infinitely replayable because of mods. I can ignore Oblivion's really underwhelming main quest for more than 150 hours of extra gameplay, and I've much to do in both titles. That said--if you plan on getting Skyrim, consider getting some mods for Oblivion to do something different. It's a neat idea you had, but don't cut yourself off from the idea of returning to the older product at some point in the future.