Having 100% magic resistance or absorption through any means would still make you invulnerable to magic. That could be a tall order, though.
I think before it was a Resistance - Weakness = current resistant situation. That'd mean you'd need 200% instead of 100% for the same effect. All that resistance stuff is done first, though, so if you don't even TRY to get any resistance, you'd be reflecting or absorbing (not like you'd need more mana, but hey) twice as strong of spells. If there are other ways to increase your own weakness, it might be possible to get reflect spells even stronger. Kinda unorthodox, I admit, but there were plenty of 100% reflect damage people in Oblivion. Maybe possible this go around for magic? But you're right, it's likely going to be pretty difficult/annoying to pull off, gear wise, unless I'm underestimating enchanting. Might be an interesting set of gear to try to make when I get bored, though.