I've been around since the browser wars, and disagree with your characterization here. Standards don't serve marketshare, they are about interoperability and documentation.
A single user-agent technology shouldn't be standardized because that user agent has large marketshare. A tech should be standardized because multiple user agents want to use it, and be interoperable. The ActiveX comparison doesn't make much sense to me.
"User agents" serve the market. The market wanted ActiveX. There were many companies and government institutions requiring ActiveX for their interfaces.
Mozilla could have implemented ActiveX btw, but they took a stand against it.
So by your definition, what does "many" mean? Is it more than one? More than two perhaps? Should it be all of them?
What if I create a browser and announce that it will not support DRM. If market share isn't important, shouldn't this proposal be dropped?
Yes, web standards are about interoperability, but the problem is that DRM being fundamentally broken it means that open source browsers running on open platforms won't be able to "interoperate", which in my book means that this can't be a standard.
I had a long reply, but when I went back and read your original comment, I realized I was just restating a portion of your original comment but with far more words. So I think I'm being unnecessarily contentious.
Standards serve the purpose of when user agents want to interoperate, so Mozilla was definitely ok with not implementing ActiveX, just as they would be ok with not implementing EME.
But if Chrome and Safari and Edge all want to interoperate with EME, they're going to do that. Whether it's a W3C standard or a WHATWG standard, or an RFC, or a IHateFreeSoftworeSociety standard doesn't really matter. It's just whether W3C wants to be part of the conversation or not. I see little benefit and little downside to having it be a W3C standard vs. anything else. Or even for that matter, whether the term "standard" is used; even if it's somehow disallowed it's still the same situation.
A single user-agent technology shouldn't be standardized because that user agent has large marketshare. A tech should be standardized because multiple user agents want to use it, and be interoperable. The ActiveX comparison doesn't make much sense to me.