Balesir
Adventurer
Yep, this is one reason I don't want "fudges" like "well, it's OK for fighter-mages but the general rule is you can't cast in armour".And then every wizard will take a level in fighter just to get the ability to cast spells in armor...
No thanks, I'd much rather not have the obscene five-class-characters in the game.
The real question is "should spellcasters be able to get AC as good as a fighter's?" My answer is "yes, they should, but at a cost in character resources terms, whereas a fighter gets it as part of the class". Whether this AC is gained through heavy armour (bought with proficiency feats), magic equipment (e.g. bracers of defence) or "always on" spells (effectively spell slots spent to have Mage Armour up permanently), I really don't mind. Provided we don't get any lame "Mage Armour is a ritual that needs a 100 gp focus to cast and lasts 8 hours" (without using up any spell slots at all) it'll all be acceptably balancable, as far as I'm concerned.