Content Steering is implemented in most if not all major player libraryies that support HLS and DASH (HLS.js, DASH.js, Shaka-player, video.js).
We encourage EXO Player to implement support, or signal if they would take a contribution that implements it.
Client behavior is well defined with few caveats (like when to pause steering manifest refresh) making implementation on the client rather straight forward
The manifest format is simple, but how to steer and distribute traffic is open-ended and the spec does not offer guidance
Not many commercial video platforms offer Content Steering as a service