Also, how long is long enough? It wouldn't be bulletproof...
Long enough to detect the situation maybe. New coins could take a month or a quarter to mature and it would still not be too outrageous for a mint and sell business -- resource miners everywhere have to deal with futures for such timespans.
New coins need 520 confirmations already - which is almost 9 hours.
But this is NOT the problem. The problem is that transactions from an orphaned block get REVERSED (eg. you deposit YAC to exchange, wait until the exchange credits you the deposited balance, block gets "magically" orphaned - and you now have both your YACs AND credit at an exchange - that's why Cryptsy has been disabling YAC trading lately).