So, I have a player who wants to make a dragon Eidolon, but, ultimately, he's just not thrilled with the breath weapon evolution. Yes, d6/HD damage seems really cool, but for a 4 point evolution, it's a little bit weak, and it's really disappointing to only be able to use it once per day.
The thing is, the cool part of a breath weapon, for many of the creatures that have them, is that they're usable so often. They aren't SLAs.
So, I'd like to suggest that the damage be scaled back (maybe a d6 every other HD), and the frequency of use be increased to once every 1d4 rounds like a dragon.