Most of the discussion was decades ago. I've been playing around with Orbiter since it was new (and back then the hardware reqs to run were very expensive, not so much today). (edited: to emphasize, I've seen a lot and read a lot and played a lot, but am not an authoritative member of the orbiter community, none of this is private nor it is official, and its greatly summarized)

The base game is workable but it really depends on 3rd party addons to do your planning and calculations and have somewhere to take off from and something to fly and somewhere to fly to.

The 3rd party addons were often FOSS licensed and despite much noise about the glories of FOSS, never got much public help, typically. A 100 dev sized project benefits greatly if a 10 dev company releases it under a FOSS license and 500 people step forward to help. A 2 dev sized project where nobody steps up to help the original dev for some decades doesn't benefit much from FOSS despite in theory "it could have happened".

There was a fear that the game being only playable with 3rd party mods, and FOSS being famous for forking, the overall project would die if the overworked single individual 3rd party devs were smacked with having to work against uncountable forked versions the 3rd party devs may have never seen or even have hardware to run (like a port to a phone maybe). The whole project can only move as fast as the slowest dev if its only usable in toto as a flotilla. Its not a game with DLC, its more like a API with a huge collection of compatible software that'll only remain compatible if nothing changes.

If you're familiar with minecraft or rimworld or similar heavily modded games, imagine if you took "everything" out of those games and put it all into addons such that they were essentially unplayable without the addons. Like imagine if vanilla MC didn't have mobs or tools or blocks, it just rendered steve in an empty 3d world.

So if FOSS didn't supercharge development, it would be useless to the overall project because pragmatically nothing happened despite the relicensing work, and if it did supercharge development, it would kill the project by wiping out the 3rd party devs whom are very handwavy the limiting factor.

Ironically as "complete" or "finished" software the core project doesn't or didn't need devs anyway. The "cool stuff" all happened in mods and addons. Want a new MFD? That's an addon. Want a new vehicle? That's an addon. Want a new system, like the complete model of an electrical system for some Mars thing I remember a decade ago? That's an addon. Want new planets and solar systems and stations and satellites? That's an addon. The base system is kind of a a window manager (yes I know its not "a window manager" per C++ code, but I mean conceptually it herds the cats of addons so they don't step on each other and generally cooperate and render to the screen). The base system needs significant development as the graphics APIs are two decades out of date, but for two decades there wasn't much to do that wasn't being done in mods anyway.

If everything is an addon its not clear what the base system could evolve into anyway. You could add multiplayer and commo, but that's best done in an addon. You could add mission video recording but that's best done by the video card and OS. I guess you could tidy up some addon API issues causing mass incompatibility issues so would it be worth it?

Much as the author originally feared, a dozen or two posts into the forum FOSS announcement and there's already talk about branches and forks and competing strategies for conversion to 64 bit that'll kill the 3rd party addons and mods that made the game usable, so the FOSS announcement is probably more an announcement of the death of the project than some kind of rebirth.