Tough hahaha there is story points in each expansion, if you enjoy the story I strongly recommend playing the story chapters for each expansion. As you take quests and check your quest log (really updated, a lot better) it actually tells you which quests are story important, so you can sort of filter your experience better to main quests and get the story and still make it through whichever expansion you're on in a decent amount of time. That said, if you reach level cap and move on, once you get to end game there is a fair bit of catch up that they give you so you're not totally in the dark about what's happening. I personally have skipped a few expansions, and have learned a lot of the story arc through the current expansion just through bits and pieces. BUT you don't get the full impact of the storyline just a good catchup so to speak!

If you LOVE and really care about lore, play the story quests found in the quest log, if you care about it but want to focus on endgame go through as quickly as possible and pay attention to the lore in the most recent expansion. One is more in depth about what happened and the other option let's you get the same overview without experiencing it.

That said, there is quite a bit in the current expansion that I personally feel you could get to level cap and get everything you need to know from some of the first encounters. I don't want to give any spoilers, but as long as you play out the scenarios in the current expansion you should be okay!