Ryan will eventually get around to the Grand Exchange, but as for now that's not his top priority. Northpole will in Blitz,in fact, it already is. But of course, Ryan will need to code in the NPC drops and all of that. Regarding the Party Room and Camp, I can see them both in Blitz, if not, at least one of them. Things I know won't be added are commands such as ::lumby, ::etele, ::fally, etc., as the magic spell book's teleports will fully work.
Here's my suggestion though; add in Camp but control it. Don't make it spawn 40,000 NPCs that are in the wall and in buildings like it is in Classic. Then possibly, modify it such as NPC drops, maybe newer NPC's, since the last time any of that stuff was modified was back in 2006.