Changing fields is though for everyone, no matter how talented you are. There is a great chance he will fail. On the other hand, he meets all requirements that are needed to succeed.

Carmack has proven his extraordinary technical skills. I recommend following his Twitter. Sometimes he posts non-obvious technical stuff. I read some interviews and to me, he doesn't seem to be a person who is driven by gaining popularity.

I think this news is very optimistic, as yet another intelligent, talented and hard-working person is joining the field. Moreover, he is a household name, which may lead to benefits like popularization of the topic, gaining investors attention and so on.

I will keep my fingers crossed for him :).