How about a compromise?

[Sotek]

My 0.02~

Facts:

We currently have caps because there is nothing beyond the content.
People who currently don't do Coil, in all likelihood, are not going to do the new content either.

Idea:

Current Coil remains the same as it is, no change in difficulty, the only change is the removal of the lockout.
Duty Finder "Easy Mode" Coil has the lockouts current Coil has.

Result:

People who are going to do the new content can spam old Coil to gear themselves.
People who aren't going to do new Coil can still do old Coil.
If "Casuals" want to progress iLv90 faster, the challenge themselves with old Coil.
"Casuals" become better at the game as a result.

Other note:

Gear from Coil presumably isn't even going to be that worthwhile anymore, what with new Tomestone and new Coil gear. Mythology should lose its cap as well, with the introduction of new Tomestones. There is also the possibility of them adding new crafted gear in the iLv80~90 range; with Materia that should be great, and we got tV matter from the main quest last update which is redundant at the moment, hint hint. My point here? Current Coil gear shouldn't particularly matter to people not doing it, Mythology/craft/etc gear easily fills that hole. The point of making Coil easier is so they can progress the story.