Personally, I'm all for them adding one.

While I personally enjoy the main story quest experience, not everyone does. There are many players who skip all cut-scenes and just try to rocket through the plot as quickly as they can. Why not just let them skip it entirely? Who exactly is benefiting from uninterested players being forced to wander back to the Waking Sands for the 100th time, only to teleport away and then skip more dialog? To be frank, I don't lose anything from other players not enjoying the story. I do, however, have something to lose from players getting bored and not queuing for high-level group content. If players want to skip most of the leveling/story, I say let them. They'll still have to level their way through Stormblood. Let the player enjoy what they want to enjoy.

As much as I love the MSQ, it's also the bulk of the problem here. There are 346 ARR Main story quests (counting the patch content), in addition to 129 (currently, there will be more) Heavensward Main Story Quests to dig through, before getting into Stormblood. That is like being forced to play through two entire JRPGs worth of content before being allowed to access the game most players are enjoying. If my friend told me "Hey, play this game with me, but first beat two entire games", I probably wouldn't want to join in.To be frank, if we don't nip the issue in the bud, it will grow into a massive barrier for new players. For players interested in the Heavensward classes, it already is. Players don't like being told to play through 50 levels and 346 MSQs using a Job they don't like, just to access one they do. The lifeblood of any MMO is new players, and we need to make sure FFXIV stays accessible.

So, while I personally wouldn't skip the MSQ myself, I think it should be an option for new and/or returning players. If those players just want to dig into Stormblood, let them. Let them enjoy the parts of the game they want to. If they decide, after watching whatever summary cutscene/introduction that they do want to experience the whole story, they can always just go back and build a new character.