Bungie recently hinted at some of their future plans with vague wording but one thing was crystal clear - Forsaken content will get vaulted in the future.
Forsaken is easily the most loved expansion and era across the entirety of Destiny 2's existence. Some would say it's the best overall, ever since the franchise started but it would definitely be a close race with The Taken King.
With that in mind, it is easy to see why Destiny 2 players would not like the vaulting of this content, on top of the fact that they paid for it once upon a time.
Still, this will eventually become reality as Justin Truman, Bungie's general manager, pointed out. He spoke with Eurogamer recently, revealing some of what the future holds for Destiny 2 and when asked about content that will be vaulted in the future, he had a flat response about Forsaken - that content will be vaulted at some point.
Bungie did already note all content is subject to vaulting and returning but it's highly unlikely players will be fine with this policy - these are the expansions they paid for and some of the content is still highly engaging. Removal of the Menagerie is one good example of a beloved activity that was vaulted.
The devs' reasoning here appears to be that they don't want overarching storylines to be happening at the same time and they are aiming to curate the experience overall.