James Fender's page

The wizard not being aloud to wear armor was a way to balance power with the fighter.
Arcane spell casters usually don't have the strength for armor. It just seems right to me. Although way back in ADND the NPC Grey Elves, High Elves and Drow Elves could wear metal armor of their own racial crafting.

The untrained penalty is a good start.
Maybe the armor check penalty could apply as well.
At least on the spells that require a somatic component. And if I remember right, DND 3.5 doubled the armor check penalty for the swim skill. That might work here as well.

At the least in the meantime it would give the development team at Paizo time to work on problems that affect game play as a whole for all classes. It might also give them the time to create updated Paizo versions of classes like the Sword Mage and the Beguiler.

Lightening bolt

35 ft radius burst centered on the caster – sphere – Like a fireball out of water

damage is 1d6 per 2 levels of the caster. Ref save for half. Minus Evasion.
Caster is within the area of effect.

This assumes the caster may cast while underwater.