Could just be a new cast of characters that branch off from there and based on certain story progress their interactions with you could be different. I think they already have some of this with different dialogue depending on certain quests your character did or didn't do.
FFXI pretty much did this with some of their expansions. Most of them branch off to another area that isn't technically a continuation of the previous story line but are related in some way.
I mean even if you play like this and ignored 3.0 something tells me you wouldn't have some of the roulettes unlocked anyways and because of how content unlocks work in this game it would eventually come back to bite you in the butt when you can't access something because you didn't do any Heavensward content.
