"Will any other vendor be able to join the board"
A slightly more hostile version might be "Why aren't other vendors in the founding board". DiBona's answer is revealing - "The only thing that's going to prove neutrality will be time" - time and other vendor representation to keep Google honest. With Google the only vendor on the board, neutrality can't be taken for granted - in either the short or long term.
I don't see this foundation being terribly helpful as long as it looks like a closed shop.