Valve do rock, and this just proves it. I, personally, won't buy L4D2 unless they can cross-play it or unless they reduce the price for people that own L4D1 (this would only work on the PC, of course, but Valve tend to reduce prices for PC players vs. 360 players; just look at the DLC for L4D1!).
It's nice to see that they're actually trying, but something makes me think it's a publicity stunt and they're just doing it so that the L4D2 boycott would disappear. Valve are a fantastic company, but was the whole "Half-Life 2 stolen" thing ever proven?
And as far as the old characters in new places thing; I'd love that. I don't really care about the lore, and they could just take out some of the map-specific dialogue for the old characters in new maps, or vice versa. It's not as though the game is realistic anyway, with bullets being fired into team-mates and them saying "Ouch!", etc. As long as they kept the map specific dialogue for the new characters in the new maps, then for me, it doesn't matter.
Regardless, keep up the trying Valve!