Valve and Nintendo agree on a collaboration game and bring Steam to Project Cafe.
Probability: 1. Unless Sony and Valve have a serious falling out and the stars align at one E3, this will never happen.
Impact: 10. This could probably bring about a fucking golden age...
Episode 3 will not live up expectations.
Probability: 9.
Impact: 0. Valve fanboys have built this up as gaming's second coming of Christ, and it's for an episodic game for a franchise that has been out of commission since the Orange Box. Tech has changed, and so has Valve. It won't be what they were expecting. But it'll still be good, and it'll still sell well.
Nintendo not only re-releases Earthbound, but also translates Mother 3 in a single 3DS cartridge.
Probability: 2.
Impact: 8. Fans have been waiting a LOOOOONG time for both of these. They haven't even put Earthbound on the Virtual Console on the Wii Shop Channel. Both happening at once would not only be near impossible, but very well received.