I agree that Game Mode/Difficulty should not be tied to Level. It'll make more sense to treat Levels as a milestone achievements (eg playcount like CXu pointed out).
Someone can come up with new medal names at each milestones (+extra reward aka "2 days supporter" @Lv50). If that's too troublesome, I reckon the existing forum titles (excl. special titles) are "rhythm enough" to be used as medal names, with Rhythm Incarnate being Lv100 and beyond. I forgot how many forum titles are there and what they're called so someone else will have to fill in that info =.=
Someone can come up with new medal names at each milestones (+extra reward aka "2 days supporter" @Lv50). If that's too troublesome, I reckon the existing forum titles (excl. special titles) are "rhythm enough" to be used as medal names, with Rhythm Incarnate being Lv100 and beyond. I forgot how many forum titles are there and what they're called so someone else will have to fill in that info =.=