Actually, we don't know which kernel will be used finally. Oleg reported that he has had an engineering sample of RT-N16 and firmwares based both on 2.4 and 2.6
http://wl500g.info/showpost.php?p=132818&postcount=528
http://wl500g.info/showpost.php?p=136257&postcount=789
At least we know for sure that asus tests 2.6, however, we can only hope that it finally chooses it...