Don't need to be done at Mojang, it can be coded on the serverI think that'd have to be done at Mojang.
queued logon has been used on Primordia since release http://primordia.blocktopia.net/queue.php was used a lot at first, not as many people getting on lately thoughi like this idea though i dont know how possible it would be. i do think a simular idea was tested on SMP at some stage