Ah, so we are thinking about more uses, rather than more flavor or more power. Well, there are plenty of convoluted racial powers out there, namely the racial spellcasting and aasimar 3rd level abilities.
We can just make it scale to keep the power level relevant. We can go from something that seems appropriate for a level 1 racial cantrip
Bonus Action, 5ft range, 1d6 damage, at-will
And the add onto that a different ability that's a 15ft cone.
Empowered Breath
Starting at x-th level, your breath becomes more potent. You can use your Empowered Breath a number of times equal to your constitution modifier (minimum 1)
Then we can add a 5th level ability that increases the damage or improves the action economy (part of the attack action/reaction)
Superior Breath
Your Dragon Breath and Empowered Breath damage is increased by 1d6, and use your reaction instead of a bonus action.
This means we don't have to use any confusing scaling or worry about the curve. We just add a new ability with level-relevant power when we need it. 1st, 3rd and 5th level seem appropriate places to add these.