It's funny how people try to make "standard" mean something magical when it's not. An Internet standard is just a document written by a committee of people who intend to do what it says. They then publicize it and try to get people to go along with it. You can't keep people from getting together to write a document or from doing what the document says. You can just choose whether to participate.

If W3C chose not to help write the DRM standard, the browser vendors could easily create a new organization and write a standard anyway (as happened with WHATWG).

Browser vendors and website authors could then read that document just as easily as anything published on the W3C website, so there is no "burden" for them. There would be no difference to the end user. The only burden we're talking about is the inconvenience of setting up an organization to do the writing. It's a minor speedbump at best.

The upshot is that there is no way to prevent browser vendors from standardizing anything they want. It only gets blocked if they disagree.