But where do I go from here? Is there something usable for the end user (like the settings app they mention) or is it developers-only for now? How do I use it with my Ableton + external setup?

The documentation I found is not very clear: https://microsoft.github.io/MIDI/

These "Deferred procedure calls" are ever present and make windows audio completely unpredictable. Having random audio buffer underruns because your video card decided to do something that stopped the OS from sending data to your sound interface is really a big problem.

https://www.sweetwater.com/sweetcare/articles/solving-dpc-la...