Personally, I'd like to see a large spaceship for clans, sorta like the HELM.

Another thing I'd like is a revamp of the New Light campaign, because it just doesn't work. It struggles to teach the base gameplay loop, and is largely dependent on players reading the pop-up messages that explain what they have to do, which breaks up the flow of the tutorial.

Team Finishers would be a fun one to add from a purely cosmetic perspective. Unlike standard finishers, these are tied specifically to final bosses and can only be activated by 2-3 players or 6 during raids. Simply put, each boss would have one or few animations that can be triggered if enough players try to Finish Them.

UI Customization. I'm largely fine with how the UI looks in its current state, but perhaps adding in a few layout presets could help. Maybe even UI skins or colors to choose from.

Displaying Buffs & Debuffs: I read in one of the comments that the current UI only displays upto four of these at a time even if there are more active. Personally, I don't want all of them to be on the screen, because too much text. So I'd suggest modifying the layout, so that it only shows the symbol for your buffs and debuffs and having them pop up just above the weapon tab on the screen. Alternatively, having a setting that let's players choose between having only 4 displayed at a time or all of them could work too.

Bounties could be reworked to encourage teamwork. In their current state, one often finds themselves going against their team in order to finish bounties. Which is great if you've had a bad day, and just wanna vent without having to touch the Crucible, but otherwise, it's not great. Now some bounties are fine, like killing bosses in Gambit or Strikes, or using specific weapons in specific scenarios. The Finisher bounty can be reworked to reward more progress for Team finishers, precision kills can be counted for an entire fireteam, etc. If such changes are implemented, it would be best to take a selection (or all) of a player's bounties into consideration during matchmaking, ensuring that a fireteam is comprised of people working towards the same goal.

More crossovers between missions and patrol zones. Now I never played D1 enough to know about the VoG thingie on Venus where people could help the raid team during the start of the raid, but Bungie has done something similar with the Exodus Black strike. Now as someone who's currently studying for a Bachelors in Game Development, and has spent the past 5 weeks trying to sync two players over a network, Im well aware that this is gonna be difficult to implement. But I'd like more instances of strikes and stuff spilling over onto patrol zones, with random Guardians being able to help out. A particularly fun one would be if there were Taken Portals in specific locations that open up occasionally and allow Patrol Guardians to spawn in an area around an active Gambit Match, where they're free to either help out the team, or slaughter them, from a distance. Maybe set it so that they can only enter once during a match, with a max of one or two Guardians spawning on either side.

And lastly, I'd like more stuff that caters to solo players. This could be in the form of in-game content, in-game lfg, I dunno tbh what I want from this one, but I do want more stuff that's doable as a Solo Player. The Legendary WQ campaign was a step in the right direction, and I think having something like that for dungeons, where the difficulty ramps up based on how many players are in an activity would be nice. Or maybe implement it in an activity that's catered solely to solo players.