For those replying with "XML is bad and therefore Google is right", reading the whole thread presents a more complex picture. Quoting from various comments in that thread,
> this is a proposal for querying the HTML DOM with XPath, not XML.
> Per https://www.chromestatus.com/metrics/feature/popularity it does seem that about 1-2% of page views end up using XPath
One could argue whether a feature that has existed for over a decade and is only used by 1-2% of page views is worth improving, but that is not the argument that domenic is making here.
> Chrome is not interested in this. The XML parts of our pipeline are in maintenance mode...
> By "XML parts of our pipeline" I mean "everything implemented using libxml and libxslt".
His comment is that in the Chrome codebase, the XPath implementation is within some XML libraries, which are in maintenance mode. This may or may not be true for other browsers. It's interesting that these refer only to the implementation cost to Google, and does not make any reference to costs or benefits to other users of the web platform, which are discussed by other comments.
Overall, while there seem to be valid arguments both for and against the proposal, arguments for are being presented publicly in that thread while those against are being discussed elsewhere (perhaps at Google?), with only final, unchallengeable decisions being posted here. Domenic is fairly explicit in his refusal to engage in a discussion.
> As such, I won't be participating in this thread further. I think I've made our position clear.
Irrespective of whether you agree with the proposal itself, to an outsider like myself it looks like the process of discussion does not exist at WhatWG anymore, and that Google basically dictates terms.
Edit: moved a paragraph for clarity