64 bit would be very important for me, at least. I've invested fairly heavily in some really nice but RAM-hogging sample libraries powered by Kontakt; one of them, in fact, a great acoustic guitar library, basically consumes all spare RAM on a 32 bit system, once you take into account the RAM needed just to run Windows. While I can always audition things in BIAB with SampleTank or Coyote Forte, imagining how they'll sound when I export the midi into my DAW and play it through my Kontakt stuff, it's not ideal. If I could do it from within BIAB, that would be a serious workflow boon.