The standardized protocol already exists and it’s called DLNA which Chromecast initially cannibalized in its first release and then basically killed off every single other DLNA provider and app because they Sherlocked the feature into the Android operating system and to the Chrome browser.
Now that they are at risk of being split up for their monopoly, and as they lose an Antitrust case for their search monopoly, they are probably looking to kill off the Chrome brand because Chrome is how they entirely dominated the web, warping it to their standards and killing more open standards in favor of their Proprietary technology.
DLNA is meant to play media from a media server on a home network. It doesn't make sense for Internet services to implement DMS. The relevant standard for casting using web protocols is DIAL.
I vaguely remember DLNA... Which is to say, I remember it barely working at best and mostly just wasting a lot of time debugging configuration and network nonsense.
Arguably the biggest advantage of Chromecast was just not having to deal with all that.
Now that they are at risk of being split up for their monopoly, and as they lose an Antitrust case for their search monopoly, they are probably looking to kill off the Chrome brand because Chrome is how they entirely dominated the web, warping it to their standards and killing more open standards in favor of their Proprietary technology.