I think it probably is going to take a long time to mo cap hd replacements for the old characters as TRMK.org has suggested, but I don't know if that would be a reason to delay an entire announcement of the game, maybe just the release date.

I think the real reason there hasn't been an announcement for the HD Kollection is because one very big draw for the Arcade Kollection is the MK2011 Demo. With the final build of MK2011 not even scheduled until sometime next Spring, I think its A LOT of pressure to ask for a working Demo by a set date before 2011. In fact it may be something that they are finding is out of the realm of possibility and they want to hold off any concrete announcements before they know for sure.

Or maybe they just love the suspense