IMO what is going to happen at some point expansions will include a skip potion once SE consider is more likely that people leave than stick around. You can say whatever you want, yet in reality, the game is designed to be played by a wide arrange of players and some just want to play with their friends.

And is sad because giving skipping potions is not the solution. From my point of view not making each expansion independent was a mistake, why I mean by this? Simple, keep everything like it is today but once you hit 50 with a class you can jump right away to HW, continue with ARR or mix both if you feel like it. Same for everything else. Want to unlock everything from an expansion? Finish the relevant MSQ and side quests. Want to rush to the latest expansion to play with your friend? Go ahead, you can always continue with ARR/HW/SB later on!

Sadly I know is not going to happen because at times certain MSQ require to revisit locations from other expansions.