The Metabreath feats don't require a recharge in rounds explicitely. Clearly, that's what they were primarily designed for (since this is what dragons do), but I find they work fine as is even for sorcerers which replace spell slots with breath attacks: in other words without house-ruling an increase in spell level slot cost. This is balanced because the fact that you need to wait several rounds between breath attacks is a cost even if you also need to pay a spell slot, and because a sorcerer's breath attack is never his most powerful weapon (if he chooses to use spells to deal damage he'll come out ahead).
I let my sorcerer simply use the metabreath feats as-is therefore. In addition to the spell slot he must give up to perform a breath attack at all, if he's applying a metabreath feat, he also needs to apply it's cost - namely an additional waiting time after using it before using the breath again.
It's nice for the player, because he can use a variety of breath weapon feats without wasting all his high-level slots, and it's nice for gameplay because if he chooses to do so (at the cost of one or more feats of course), then his signature ability (the breath weapon) can't be used every round, and that makes for some interesting tactical situations.
No need for a house-rule, although the rules look a little funny, they work fine as-is, I think.
