I also think that it will be cheaper for google to create a new Ebay than to buy an old one whole Ebay consists of 1% software 99% brand Google has the more powerful brand than ebay. So they can promote a new auction site very easily.
ComScore's september traffic had ebay at 237 million uniques and YouTube at 81 million uniques so Youtube doesnt even get more traffic then Ebay according to that.