That bit of answers made me more confused. So for those who are in coil now, and having Extreme modes be part of the main story after TitanHM, does that mean Coil will be locked for everyone after the patch has been implemented?

Because after relic reborn quest has finished it unlocks coil, main quest story follows

Relic Reborn > chimera > hydra > ifrit > garuda > titan > 900phil item to make +1 > coil.

now its;

Relic Reborn >chimera > hydra > ifrit >garuda > titan > INSERT 2.1 PATCH > Coil

this makes no sense if my understanding of the answers was correct.