if i look at the past expansions that i bought (and i consider the LSs as expansions as i had to pay gems for new content) only very few wow moments from maps come to my mind. HoT definitely got me with the jungle environment but i love playing rev, especially herald and that's PoF as well. also my so far only legendary is a HoT legendary. after that, the maps never were a selling point to, me neither **before** nor **after** buying. i didn't expect a lot and didn't get a lot. vabbi is the worst map imo, kourna, jahai, thunderhead peaks, lake doric and especially istan come close. oh they're mostly PoF/LS4, but dragonfall, sandswept isles and the desert highlands are actually good ones.
so would i buy an expansion without maps?
why not? maps after HoT weren't even close to core levels, though a big part of that is their design for mounts which made at least half of the PoF and later maps ugly and unfun. why does kourna only offer 2 wps even though there are at least 2 more obvious wp spots and the map is big enough for 10+? because rollerbeetle. why is istan packed with annoying enemies in every single spot? because on a mount it doesn't matter. et cetera et cetera.
i would instantly buy a new expansion which offers maps that never allow mounts because i believe those maps will be beautiful and fun.
i would, however, also buy an expansion without maps, those aren't any selling point to me.
i do agree on previous posts that an expansion that clutters old maps even more would do more harm than good. be new to the game, start playing some story and whoosh there comes an awakened invasion! who are these, where do they come from? hey and look at that boss marker on the map! oh it's a bloodstone crazed creature that instant-downs you because you lack the mastery from 10+ years in the future (ingame..). more of that is not good, especially since the story told by those events is only present for us who have been active when it was added. the context is lost to anyone in the future.
what would be the biggest instant selling point for me?
imagine an expansion that adds a new UI entry to character creation to create a non-commander. that character has no access to LS2, HoT, LS3, Pof, LS4, IBS stories but it has a new lvl 1-80 personal story that is woven around the old story, maybe you see a commander that looks like your most played character at some point as you'll be someone in the pact to best zhaitan. that story can then continue after core tyria and expand on expansion maps _in any imaginable order_. it might be that you're not part of the pact fleet but instead travel to bitterfrost for a kodan quest, then visit elona just to hear that a bloodstone exploded and rush back north to bloodstone fen, finding the pact in an awful condition so you move into the heart of maguuma to help out. it's all possible and every non-legendary story is welcome. just a traveler/adventurer that finds itself thrown into the normal story from time to time by totally unrelated reasons.