I actually think Iguanas should get out of these boxes, they would work great as habitat species.
For other reptiles, I belive a sea turtle would be nice, specially if we get aquariums. There are also some fresh water which would be suitable (some softshell, Podocnemis,...) and some tortoises too (specially the spurred tortoise). I highly doubt they will get some animations for snakes and the only monitor that should be big enough is the water monitor (which probably would be an easy reskin of the Nile monitor), rock monitor, the Perentie and the crocodile monitor (which would probably take a lot of time, as it's mainly an arboreal species).
For crocodiles, I belive the American Alligator is really a must, for most of the community. I would definitely prefer an Dwarf crocodile and Tomistoma, but seem very unlikely to ever see these in the game.