24 man raids beyond their current difficulty would be an absolute nightmare that'd essentially be restricted to large FC's.

While it would be nice to some 24 man raids in the style of HM dungeons it's just not feasible. Even the braindead easy ones like the Crystal Tower raids can go horribly south if people just decide to totally disregard all mechanics which is something people try to do now with Rabanastre which is at least semi-relevant still.