I think it's just the design philosophy Yoshida has adapted to the literal point of "play the way you want to play" but of course it has it's limits. When it comes to the MSQ while it won't be right away it seems the plan is to have it all setup by 6.5? So ARR-HW-SB-SHB-EW somewhat soloable but with certain parts that will require MMO interaction.

See I think one misconception being made is that this change it's not so much about making it a solo MMO, it's fixing an issue that has plagued the game for a while and that's people who want to enjoy the story but are unable to play the game at their own pace because of people who are rushing through roulette to get it done. There are a lot of story dungeon bits that players can't enjoy because veteran players just wanna get it over with, so those new players lose that atmosphere that the veteran players got to enjoy.

So by adapting this solo mentality into older content, it gives them a way to introduce players into the game and allow them to truly play at their own pace, where they can explore dungeons at their leisure without feeling like they are being tugged by the leash to finish it as fast as possible.