Didn't Chromecasts work with DIAL which was an open protocol?
https://www.dial-multiscreen.org/dial/protocol-specification
The DIAL spec documents spend three pages talking about discovery and sixteen pages talking about state tracking, launching, HDMI-CEC, etc.
It's a pretty basic protocol spec since it mostly relies on things like UPnP for discovery and HTTP REST so a lot of complications are already defined in other specs.
Matter Cast has what to me are previous limitations:
1. Connecting clients can only talk to existing Endpoints running on the target device. If I use Tidal for example, the smart speaker or smart TV needs to already be setup with that app, and needs to be willing to let a background service run & register itself with the platform. https://github.com/project-chip/connectedhomeip/blob/master/...
2. Only native apps are supported. There's no protocol to say open a webpage & control that.
3. No support for multi-party sessions. Only one user can interact at a time.
4. No support for the Web's Presentation API. Since it's not based around urls & web pages, it would require lots of additional work to make it support the standard web pages have to spawn a remote display.
By compare, Open Screen Protocol lets any target device open any web page, which is very similar to how Chromecast development works today. Whether the target device is Android, Apple, WebOS, Windows, Tizen, or other, the expectation that I could Open Screen Protocol cast to it remains the same. Where-as Matter Cast requires a native app on the device & the app has to be installed & potentially even greenlit by the target device platform itself.
OpenScreenProtocol really looks to have it all, & the model is so much more universal. Really wish we saw some device makers pushing for it these days.
Amazon is pushing Matter Cast, which is in many ways superior to Google Cast, most of all by being open. Its biggest downside is that it's not supported by anyone else.