People who dislike the grind to Heavensward or Bloodstorm aren't concerned over leveling. Plenty of these types would have that done within a few days. It's the MSQ itself they find tedious because you can't veer away from it. You must progress through the entirety to unlock the expansion(s). Your example of WoW isn't accounting that is precisely why they went ahead with a skip option. If FFXIV were open ended right from say, level 20 or even level 50, people wouldn't complain. In fact, you'll notice very little complaints regarding glamour being only unlocked at 50. Why? It's annoying, but you just have to grind then talk to an NPC and bam, glamour away to your hearts content.
Now is it too early to consider a skip option like this? I'd say that is certainly up for debate. Seeing I don't play WoW, I cannot directly compare where their content bloat became enough of an issue. The concern on FFXIV's side is just how much story there is to access content. You really cannot do anything except story, lest you be gated off. For those thrilled at the possibility of playing Red Mage. The frustration of having to play through two full games just to then level the job they actually want may burn them out.
Another reason to consider is how frequent do we see or even tell people "the game gets so much better at 50?" Unfortunately, classes are not well designed. Impulse Drive and Stone I spam come to mind. FFXIV, at least in my opinion, shows off arguably its worst qualities at the early portions of the game. Some are more than happy to deal with it or even enjoy it. I, personally, didn't mind the baby leveling. Others aren't. Frankly, I think you could make just ARR skippable but still require Heavensward and plenty would be okay with it because of the aforementioned reason. If there were a way to skip the patch cycles, that too would help alleviate the grind.
As for the cash shop. You admitted yourself, people still vehemently complain yet grudgingly accept its existence. A potion skip would be similar. The few who did quit as a result of its inclusion would be replaced by those who purchased said potion. Most would just continue playing regardless though.
Actually, a skip potion would be a direct hit to their profit margin. RMTs typically charge upwards of $200 to level you from 1 to 60. Square introducing a skip potion for $35-50 means its more cost efficient to buy from Square than RMTs. Plus, you aren't risking your account. RMTs also aren't going to spent $50 for a hundred bots to reach Stormblood because that works out to being thousands of dollars without a guarantee they'll make back that profit.Should I also note that this opens up a new avenue for RMT? They're not afraid to invest some money already. Now you've given them a pass to new places so they can screw the prices of new stuff like newer mats. Until SE puts in an effective method of eliminating illegal RMT, I'm against the idea. WoW at least added a method to legalize it.
And none of this accounts for what restrictions a skip potion would have. WoW implemented a "Proving Grounds" that forces players to do certain amount of content in the same sense we have Hall of Novice. Except in their case, you had to dungeons and whatnot. Bots have a much harder time getting through decent leveled content because, for one, said content will murder you if you don't play properly. People are also more likely to notice their antics and kick them.
Yes, however not without cost. Any trimming of old content requires script rewrites and new animations to keep the story cohesive. Imagine if 2.1 to 2.3 were merged into 20 quests. Despite the multitude of filler, there is still lore tidbits and three Primal fights they now have to rework into a third of the quest requirements. All of this extra cost would be subtracted from Stormblood's budget. In essence, the devs are tweaking content none of us will ever see unless we level an alt. If that cost is minimal, then perhaps it's worth exploring. If it isn't. Well, I don't want them spending money on stuff I won't even see.Can the story use some trimming? Yes. Why do I have to help a paranoid ex-Garlean kill bugs and tigers? Why not lower the amount of items needed collecting and merge quests? Have him make you kill two swarms to lower the buzzing, and gather two tiger hides to help him make up for lost time? Why do we have to keep pointlessly going back to the Waking Sands when we're wearing a perfectly good linkpearl? Why is melding part of the storyline?