To be fair, most MMO xpacs don't require you to beat the story of the base game/previous xpac to access as far as I remember. Not even XI outside of maybe needing to beat the initial story for whatever city you started in (Never played XI so not honestly sure.)

Personally I'd like to keep having to DO the story kept in to access the next xpacs story, but have certain ways to get into the new zone that don't require the story. Like Crafters/Gathers level 50 quest could give them access to Ishgard. Like Miner leads to this well enough on its on as you are a contractor from the Miner's Guild working in Ishgard. No mention at all of how you normally get there, don't even need it.