We're way beyond that point. ICANN already allows effectively unlimited TLDs as long as they're three letters or longer. So far, thousands of new TLDs have been applied for.
It's certainly an interesting question. One I'm not qualified to answer.
So unlimited permutations of [a-z]?
Sure that makes sense....
http://www.circleid.com/posts/20120506_2100_new_gtld_applica...