It's an interesting idea, and I nearly was going to post that it seemed like a good idea. However, reading it more carefully, I see the issue of restricting spellcasting based on the armor type you have.
That idea has some problems it must overcome.
Restricting spellcasting based on armor type will greatly reduce the viability of hybrid builds. Hybrid builds are pretty much a necessity because this game will have 7 INT-based skill schools, 2 FIN-based skill schools (one melee, one ranged), and 1 STR-based skill school.
Hybrid builds already will have less power than pure casters or fighters because of attribute splitting. Attribute splitting is further increased by the requirement of needing to heavily invest into Memory - otherwise the Hybrid build loses the only benefit of existing - greater skill variety.
So hybrid builds have more variety with less power. If you add on further penalties for spellcasting by wearing armor, then that cripples hybrids even more.
