Well, knowing a bit about the market, if Gemestop's stock price is going up, then they would be the company being bought out. The buyers stock usually falls during these, doesn't shoot up.
This could be interestng to see who buys them, and how inflated the price might get. I have some 5 Gamestops within 5 miles of me. There are several malls that use to have 2 in them (they finally started closing some of those ones down). I have to think anyone buying will instantly close down several of the stores and consolidate inventory.
My best guesses would be either Walmart/Best Buy/Amazon. All of them have run at least pilot programs into the used industry, they may think it makes more sense to buy out Gamestop than build their own. Walmart would be a really interesting fit on paper (not sure financially if it works) They already sell more games than any other store. Give them the whole used market, which I would imagine they are going to extrapolate to include used books and used DVD's. Walmart would have substantial influence on what you could buy (more than what they already do).
This would also get around any Walmart used item monopoly issues, since that was handled in the Gamestop/EB Games merger.