Actually, this new expansion that's coming out supposedly was to be apart of Destiny 2, but because of how much they've fucked up (including up to Taken King, TK launch, and post TK launch), they had to go back and keep adding in content or else they'd bleed out too many users before 2 gets launched.
I dropped out of Destiny just before the first dlc came out back in fall of 2014. I was in a month and quit cold turkey because you had to purchase the dlc in order to keep playing all the other end game content. I said fuck that and dropped it. The only reason I actually jumped back was a friend of mine got me Taken King for dirt cheap a few months ago back in January.
I can tell you right now that Bungie still has NO fucking clue what they're doing. The loot mechanics in Destiny are a completely different beast compared to when it first launched in 2014. They only JUST made the prison of elders dlc worthwhile again, but it's both far too easy, far too simple, and far too boring to keep doing. It's like they're trying to make a barebones MMO, but at the same time they just want to make a loot FPS game.
Honestly, at bare minimum, if they had just made a serious (no stupid meme jokes) version of Borderlands with huge maps and more in depth skills, I would have been totally cool with it. Instead, we have this amalgamation of obvious cut content for dlc, completely removed content during development never to be seen again, content that was around originally but has yet to be updated post TK launch, and mediocre content that is expected to be grinded out infinitely.
Most of the players still around are just waiting to see if anything major might happen to shake things up. There's no direction to this game, almost like Warframe. Shit keeps getting added without a thought, and then you're left with a whole bunch of older bullshit that you don't know how to tie together.
If they're just going to try and expand on the slapped together mess of a game for the sequel, Destiny 2 will be dead in the water. If they start fresh and actually have some sort of plan, then they might have a shot.
Either way, fucking avoid this at all costs.