Yep, that is definitely on the to-do list as a priority! Actually, I was just gonna use simple coins as currency, but honestly, I like your idea best.
The problem that I have right now is coming up with a good meta-progression system. My first idea is to be able to increase certain augment caps and/or initial base stats. The second is to develop sort of like skill trees for the ability-related augments. For example, the lava pools can be upgraded in 4 distinct ways (size, damage, duration, probability), as such, some of these you would have to unlock through the skill tree.
If anyone has suggestions I am all ears!