Carmack needs to be paired up with a real gameplay/product/market counterpart. His Steve Jobs so to speak. But if he is happy doing it his way then he should continue. I just hope Bethesda won't punish him for Rage's commercial disappointment.
He actually said that "there is more opportunity for technical innovation [...] in gaming than practically anywhere else I can imagine". A modern game like Rage can stimulate one's intellect for a very long time.