Basically noone other than browser vendors will look at the spec anyway. The reality is effectively descriptive, not prescriptive.
Sure, without having a majority marketshare a browser can't by itself push for their new features to be supported by other browsers, but they will effectively disincentivize website owners to not use features they don't support if they have marketshare of any significance. At which point it'd be in W3C's best interest to allow Ladybird to participate, or else their work gets underutilized.
But if there is more browser diversity, and less support for Chrome Only things, maybe that starts (continues?) the path of Chrome becoming IE6