My concern is that GenCon is too brief. I attend with two sets of friends. One set wants to primarily play PFS. The other set has traditionally played primarily 4e. Last year, given 4e's relative absence, we played mostly L5R. I would like to be able to attend Gen Con and have time to play PFS, 5e, 4e, L5R, and other games, look through the dealer's hall, and commission some sweet original art. In short, I propose that GenCon be extended to last for two weeks.
In all seriousness, I am confident in WotC's ability to have something together for GenCon. My guess is that something will be a Tyranny of Dragon's starter set. I think that the organized play offerings will also be tied to tyranny of Dragons. When the PHB is finally available (no predictions on release date here), WotC's organized play campaign will probably allow for character rebuilds to take in the new options.
What makes me sad is that the WotC organized play special event will probably share the same time slot(s) as the PFS special, and I'd love to be able to play in both.