I doubt this is how it will play out. I would expect the first two or three expansions to be part of the continuous story but we will reach a conclusion eventually and further expansions would not need to be story gated. There are also plenty of things SE can do to ease the time it would take to progress through all that story content. It's not a big deal.
Are you a new player? No? Then please don't pretend you now what new players think of having a host of content available when they start the game. This argument is getting really old considering not a single actual new player has said it. We've already identified that most of the people complaining about this are actually just complaining because their crafting alts and mules can't get free access to Ishgard.