Everywhere you see players having an egg they cannot hatch because they can't afford a habitat for the new dragon. There could (in a perfect world) be dragon nurserys you could buy, a habitat that could hold 3 lvl1 dragons while owner collects money AND can continue breeding dragons without having the nest "locked" by an egg in it.
This baby dragon habitat could be able to hold 3 dragons of any types, and you shouldn't be able to feed/level them while they're in there. Also you might not let these baby dragons earn any money while in there, otherwise surely there'd be players exploiting this and use it as ordinary habitat instead of buying a real habitat.
Well, maybe it's not even possible to put smthn like this in game, but i like the idea myself anyway!