I want to start by saying how great and rich the new Pathfinder material is to read. It made me happy to see that we had an alternative to 4e. The fact that Pathfinder has guys like Sean Reynolds and Monte Cooke and the rest of the crew on board is like having a D&D Pantheon at our fingertips. I can't tell you how monumental this is.
But...
The fact that Pathfinder is going to use the 3.5 rules at Gencon after having us read the free download and NEW rule set is really pulling the rug out from under the gamers who are clamoring to play "3.75". Its like having the go-go dancer not do the reveal if you get my drift. A real tease.
So with Pathfinder at Gencon we get to pick a faction? And now that is supposed to quench the thirst of the player? After reading all of the incredibly juicy stuff about the new race and class upgrades we get to go back to the stone ages with 3.5. Not a good marketing strategy.
What will keep folks from playing Living Forgotten Realms or even 4e? At least with Living FR they can use more than the 3 core books to make an intricate character. Don't get me wrong... I am not a mechanic when it comes to playing D&D... I adore a strong character concept and back story. But Pathfinder is going to lose a lot of the "mechanics gamers" to the other D&D options at the Con.
Marketing wise you need to consider using the new rules in your Campaign Standards for Gencon so that you don't lose the great momentum you have generated.
Right now showing us this great tease and then telling us to go "back in time to the stone ages" is really disappointing. You show us the ultimate sexy setting/rule set then tell us... "Noooo you can look but don't touch"!
Bad move Pathfinder.