For other headsets, you might be able to have some success with open source alternative software.
For WMR there's the OpenHMD project which gives only seated play, no motion tracking. There's also Monado which uses OpenHMD, libsurvive etc to talk to the hardware. It's just the compositor; an alternative to SteamVR's compositor. Both OpenHMD and Monado have 3dof controller support but neither 6dof.
For Quest there's ALVR, which is like an open source version of airlink and reportedly somewhat buggy but usable. ALVR is a bit of a mess, honestly it feels like a miracle that it works at all. For some people it seems to never be able to run for various reasons. To get it to run there are loads of corner cases and issues you'll probably have to work through and weird buggy behavior from SteamVR. But if you get it to run and have a good enough encoder on your GPU, it's pretty much fine.
Longer term, Valve's next VR headset is at a very early stage. Code-named Deckard, these are the specs it's currently speculated to have:
- Qualcomm XR2-chip handling tracking and the VR-plumbing side of things
- AMD APU handling the graphics
- 2x eMagin 4k MicroOLED displays in a diamond-configuration for wider FOV capable of foveated rendering
- Arcturus Inside-out tracking
- Eye-tracking
- Off-ear/"floating" headphones/speakers. built-in Stereo-mic. Like the Index
- Most likely some kind of option to hook it up to a pc, either wired or wireless
- Linux-based SteamOS like the Deck's running on the headset