Isn't this why we have the W3C, so standards don't get made unless multiple people benefit? This seems like Microsoft with IE6 all over again.
IE6 gave us XMLHttpRequest because they wanted it to build Outlook for the web. That seems like it turned out ok.
In general I think building browser-specific features, seeing what works, and only then standardizing is a much better path than starting with W3C.
That depends on one's definition of "ok". I don't think that modern web is ok.
That said, Portals _are_ going through the normal W3C process for experimental features via the Web Incubator Community Group: https://wicg.github.io/portals/
W3C is a joke. The modern web is, like the old web, run by the dominant browser vendor. Calling it an open standard is just marketing.
If you want to contribute, there's a repo full of issues that's completely public: https://github.com/WICG/portals/issues