Don't bet on it. Early Prescotts were 64 bit too, lol. That never panned out and this won't either. Only possible reason they wouldn't be telling everyone in the world Yonah was 64 bit is if it isn't. So take your cue there.
If they "could" get it to work maybe by stepping up the cooling to desktop replacement levels, they'll be saving that tidbit in case Turion dual core takes off and starts harming their Yonah sales.
Food for thought