It's just fucking hilarious to me that once some randoms on twitter cracked D2, all the sudden they can do things on Destiny that Bungie said would be too much work. Just goes to show how retardedly awful at game dev Bungie is.
To be fair, and this is going off of how I understand Project Sunrise to work, it's not exactly the same thing. From my understanding, Sunrise works by making a pre-Beyond Light version of the game files ignore any kind of server checks, letting it run the game without having Bungie's servers say "uh no that's the wrong version." You can load up any space or any mission and have it work without issue, and with some effort of matching scripts and spawns, full activities can eventually be rebuilt.
When Beyond Light released, the engine was updated in such a way as to make earlier content not immediately usable, so anything existing had to be ported to work in the new version of the engine. How much work that would entail, I don't know, but it obviously wasn't as simple as dropping it in and calling it a day; I think most of the challenge was in needing to rebuild all the lighting, but I'm sure there were other boondoggles. It wasn't an insurmountable task, I'm sure, but it must have been enough to where they basically never ported anything from the first three years of D2 that wasn't in that initial batch when Beyond Light launched. To my recollection, the only content that eventually made its way back in after that was The Whisper; Zero Hour; a few Crucible maps; two Gambit maps (one repurposed as an Onslaught map); and the Calus, Argos, and Insurrection Prime arenas in Pantheon.
So while the Sunrise devs are doing a tremendous job in resurrecting old content and I hope they're able to effectively rebuild everything that we lost, setting up triggers for scripts and spawns that they can easily see in the game world isn't as much effort as rebuilding entire swaths of the game for a new engine. That said, Bungie 100% could have devoted the time to bringing everything back, they simply chose not to. And I know dev resources are finite and all, but then I think about the studio construction and the incubation projects and fucking Marathon, and I can't help but wonder how much more Destiny we could've gotten if they weren't so retarded with their money.
ETA: I don't want to have sounded dismissive of the Sunrise team's efforts or imply they haven't been doing a lot of work, considering they've essentially been coding their own versions of dev tools from scratch and all. I'm sure it took a lot just to get to the point of even launching an old instance of the game, and the progress they've made since those early previews has been phenomenal. I simply wanted to bring up the fact that it's not the same as rebuilding content for the modern engine, something we probably would have seen a lot more of if it were easier to do (again, note how nearly all resurrected seasonal content comes from after Beyond Light's launch).
