Ultimately they will need to address the issue of leveling and gated content like all mmos do as they age. The better solution imo is to remove the filler quests in the MSQ by turning them into side quests or outright deleting them.
They also might want to stop increasing the level cap after the next xpac and start releasing expansions as side stories that are not sequential (ie similar to what FF11 did with many of its xpacs)
Regardless introducing a leveling potion (especially at this stage) is a lazy and honestly greedy solution that will cause more problems than solve.
