Advantages for bigger belts
Thought this already existed, but anyway:
Whenever someone upgrades belt, I think they should upgrade power, too. For example, when someone is on 7th dan, they move extremely fast and a simple tap can cause huge amounts of damage. Might seem OP, though, but also give lower belts a way to easily upgrade to that level while on something like Green Belt with some TC. Kinda like in Minibash.