I understand from Bogus post that 12-man T5 will be more demanding.
All 12 will have to be top-notch players. So 12-man T5 will be more "elitist" than current T4.
Therefore in term of audience, that will be a poor allocation of ressources by Funcom.
PS : in a 24 man raid in T4, you can have average player (me first)