Three pillar of leveling-up.

I was thinking about a PC could level-up three different collumns.

The first one would be the classic class levels. Nothing more to say.

The second one would be the knownledge pillar. This doesn't help PCs to become stronger or more powerful but to know more things, for example new languanges. It would work like background with levels.

The third one would be the "evolution pillar". It would work like adding a new layer of monster-template class. This would be for campaigns where PCs could be racial parangons, or monsters like half-dragons, werebeasts or undeads. Here we could add cybernetic grafts or monster symbionts working like special magic items. 

It might be fine, but the template (as in dnd 3) just have exact balance between bonuses and  malus, otherwise it will be unbalanced...

Or you should reserve levels for 'monster evolution' to graft monstrous quirks...

I think this idea has merit if you work with the 3 pillars of dnd (exploration, combat, roleplay)