I don't know if anybody noticed, but the wasteland is being seriously cleaned up, what with the Oasis growing, clean water, and the radiation cure in the pitt. Do you think that by the next Fallout, the wasteland might be atleast partially restored from all these factors.

Yeah. I think in the next Fallout things will defintely be partially cleaned up, depending on the time period. If it's like in the 2330s or 2340s, then yes.

I'd like to ask when do you think Civilization wil be fully rebuilt? 2900's?

Maybe a few small pockets can possibly grow back, not including "maintained" areas like vault city and the nursery (if it ever becomes canon). But for the wasteland completely restoring itself to green forests and grassy planes? No.