There are people whom have played this game since 2.0's launch who have no clue what the fuck is going on with the story. But these are the types of people who don't care if a game has a story behind it.
I remember when Heavensward just launched, the forums were filled with threads complaining about it being mandatory that they complete the 2.0 main scenario right up to Steps of Faith. Now that the MSQ for the Dragonsong War has ended, we know that the horizon for the next expansion isn't quite so distant anymore.
Personally I am against being able to purchase character boosts. Even in WoW (I've only had 2 and those are the ones that came with purchasing Warlords of Draenor and pre-purchasing Legion). WoW* can get away with this easier than XIV, since the game isn't as story-heavy. You can play WoW without ever stepping foot into a dungeon or raid, XIV is considerably different.
For the time being, instead of offering an item that boosts character levels, remove the requirement of having completed the 2.0 MSQ up to Steps of Faith. The moment that they reach level 50, let them start progressing through Heavensward content. And if they want to go back and finish the rest of the ARR MSQ, then they can do so at their leisure. And once the new expansion releases, they should remove the requirement of having to complete Final Steps of Faith in order to do the new expansions content once they reach level 60 (at least at some point). I think that's what quite a few folks want in the first place.
*I did use the level 90 boost that came with purchasing Warlords of Draenor on my Orc Mage that was level 64 at the time. Even though I was not familiar with a Mage at end-game level (at the time, I've only leveled Druid, Hunters and Paladins to max level) I did look up a guide on how my Mage's rotation should go in both single-target and AoE combat. But, again, I'm experienced enough with playing MMOs in general (having 16 years of experience doing so) to know where to look to do research on the roles that I play.