In case you didn't know, Stadia is now doing a free 2 month trial (CC required) of their Pro tier, which is what gets you Destiny 2 and all it's DLC. I decided to try it because, why the hell not, and also I know the population is super small so me and a group of friends wondered if we could get certain things done more easily, like Gambit triumphs, etc. Up until this point you needed to buy a Stadia streaming controller, or own certain Google hardware.

My setup:

Windows 10 PC with a GeForce 1080 Ti and Ryzen 2600.
Wired internet - 150MB down, 5-10MB / sec up depending on the time of day
PS4 controller connected via USB

Performance
I signed up through my phone, and claimed Destiny 2. Start up is easy, you just hit the big play button and an instance is created for you. Start up time is pretty fast, and it seems to take very little time to get to the character screen, although I assume this is more related to Stadia only having 1% of the userbase.

In game load times are great, comparable to having an nVME drive on the PC version. I went to the tower which actually had quite a few people in it. Everyone except for Founders have a Name#0000 style name; Founders just have names with no number tag after them. Interestingly, I found there is NO way to directly add friends in Stadia D2 - the 'profile' button when inspecting a player or inspecting them via the roster is completely gone. To add people as friends you either need to pull up their name from Recent Players or type it directly.

I then loaded into a patrol - almost instantly. Pretty good so far. There is input lag but on controller, it's like if you were in a really good Reach Firefight connection session - most of us that put up with that will be fine. It's -there-, but it's not unplayable.

Mouse and keyboard are a different story. While keyboard inputs feel fine the mouse is just too laggy to feel good. I gave it an honest try but went back to controller only. I highly suspect the vast majority of Stadia Destiny players are playing via controller anyway. This might be better for people closer to a Google datacenter.

Matchmaking
The immediate difference you'll notice in D2 stadia is that the playerbase is very PvE centric. Looking at the population stats on warmind.io , over half the game is in a story mission or in patrol on the platform. You'll see people decked out in full Eververse vanity gear on patrol in this plaform - something I don't really see on console or PC, where it's much more common to see those in PvP. A lot of people know how to turn every PE heroic, and you'll even see groups waiting around a flag for the event to start.

I tried a Forge, it took a while to find someone and it started with two people, but we eventually got a third. The interesting thing about Stadia is if you have everyone on the same datacenter, there's no world lag. You pick up stuff like the forge orbs instantly after holding the button to pick them up because the state host is possibly in the same building as you. Neat. HOWEVER, this doesn't guarantee no in game lag. I did see people jump around in a few rare cases. When me and my friends matched up later, one of them even saw my name as a black bar with no emblem and 0 light, which happens to us on PC, so even Google datacenters seem to have NAT issues between each other. We also got kicked once for packet loss from the world server while trying to get a Gambit match.

Outside of patrol and strikes, not very many other game modes are viable. We didn't try crucible but we did try Gambit. It took about ten minutes to get a match, and the people we were playing were not exactly great at it, even though they were 20-50 light levels above us (up in the 1010s+), so they're putting in the grind and are committed players, but not as intense as playing teams on PC and Xbox/PS4. As mentioned before, if you solo search Forges you'll often only get one other player. The only place the world is steadily populated are the destinations and the tower. I've heard people try and fail to find PvP matches before, and I'm not aware of any flawless Trials runs on the platform either.

Summary:

Pros
Picking up and just playing is nice. I don't have enough devices that can work with Stadia so I haven't been able to try stuff like switching to another display on the fly (although that might require the actual Stadia controller anyway)

All DLC is bundled in the Stadia Pro level, so the trial gives you all of the Destiny 2 DLC.

Playerbase on Stadia plays Patrol like it's endgame. If you have players in the instance they'll all know what to do. PvE modes are the bread and butter of Stadia players.

When Google decides you're going to get full res, wow, it looks like just playing it natively on a local machine. Feels like magic. Stadia is very aggressive about adjusting your stream quality in the name of keeping input latency low. Apparently there's an option to always prefer latency but I haven't found it yet.

Works natively even with a PS4 controller, which is amazing because even Steam doesn't do this quite right (if you use Steam Big Picture, it'll intercept the PS4 controller as an Xbox controller and make D2 show Xbox prompts, even though the game supports it natively)

Cons
Eats bandwidth and has input lag, which varies based on how lucky you are with a good ISP and distance to a Google datacenter. 4K can consume up to 20GB an hour. Ouch.

No local fallback, like access to the regular PC version, if your connection isn't great or if you don't like to stream anymore. Google charges full price for a lot of the games on the service - it doesn't feel like a good value proposition vs something like Xcloud, where streaming is a feature where you can buy games to play both locally on your Xbox/PC and streamed via Xcloud, with Stadia it's streaming or nothing. If Google had a PC games store I'd see more of a point to buying ANY game on the service, but currently why would you?

Mouse and keyboard gameplay is unusable.

The social features are lacking and are even worse than Nintendo's featureset on their service. Which is an accomplishment.

But hey, at least I finally finished getting Jotunn and Le Menarche while playing on Stadia:

Should anybody drop their current platform and switch to Stadia?

No. Honestly, just.. no. Stadia and Destiny 2's biggest issue is the population. I don't think Stadia has somehow magically attracted PvE centric players, it's more like it's PvE centric because it's the only viable mode to play. Cross-play would do WONDERS for playing Destiny 2 this way (and for all platforms really) but as it is it's not really a viable version of Destiny 2. This is the new Marathon for the Apple Pippin. Neat, but probably gonna be "hey, remember that port of D2 to Stadia?" article fodder 10 years from now.

It's worth checking out for free, and especially if your ISP has been kind enough to remove your bandwidth cap during the COVID crisis. If you have the internet connection and the bandwidth cap for it, it'd probably be worth it for a version of Destiny you can instantly pull up for a casual patrol or PvE grind sesh, but the game's PvP side is a dead realm. I certainly won't be paying for this one the trial ends, but my friends and I will probably be playing it from time to time for the next two months because why not, and also because we really want to see how easy it is to accomplish certain feats. But in the long run it sounds like it'd make more sense to local stream your PC version (Stadia is currently limited to Wifi anyway) or use Xcloud in concert with your Xbox version with crossplay not being a thing. It might be more valuable once crossplay is a thing (it's gonna be a thing, right? yes?), but the bandwidth cost without an unlimited plan is going to kill your wallet.