1) The stack is mature now, we know what features can exist.
2) For me it's about having the same stack as on a 3588 SBC, so I don't need to download many GB of Android software just to build/run the game.
The distance to getting a open-source driver stack will probably be shorter because of these 2 things, meaning OpenVR/SteamVR being closed is less of a long term issue.
It's possible that you can have a full open source stack some day on these goggles.. but I don't think that's something that's obviously going to happen. SteamVR sounds like their version of GooglePlay Services
All mainstream headsets get open-source drivers eventually: https://github.com/collabora/libsurvive
Also about cross compiling that is meaningless as you need hardware to test on and then you should be able to compile on the device you are using to test. Alteast that is what I want, make devices that cannot compile illegal.
i wouldnt characterize this as an "open ecosystem" though