If it's instanced, I see no reason why they would limit its availability. It likely won't even be tied to being in an FC or anything like that. The question of its availability will more likely be at what point in the MSQ can you access it. Does it unlock in ARR at a low level, or do you have to get to Endwalker to unlock it?
Additionally, instances in FFXIV are all timed. AFK in them too long and they kick you out. This might be the case with this, too, which would make it not the "sit in a chair and AFK" type of area that housing currently is.