I'm probably going to try to get a pair of the Pyramid Butterflyfish. Seems like they're seasonal - so it'll be a while before I can get them in the tank.. By time I source them, QT them ,etc... or I just get them from Dr. Reef and wait until warm weather for shipping, either way I need to exercise patience.
I'm honestly thinking of picking up a small blue tang, growing it for a few years then finding a suitable tank for it as it outgrows mine. I think if I divide the tank for a bit to let my yellow chill out, I could probably pull it off. Though if I'm dividing the tank for a while, I'm inclined to consider that Gem I'd really like to have.
A puffer or a tusk would require me starting up a FO only tank. I just don't have a good spot for a 6ft + tank and make no mistake, I'd love an 8' FO tank :)