Right. It's just funny that there is an always-increasing number of extant cases like OP's for SVG and/or internal hyperlink specs where content isolation would have been much appreciated, and literally zero cases I can think of where anyone used XML namespaces to extend either SVG or hyperlinks. (As well as the case I mentioned above where the working group apparently just said "fuck it" wrt specifying xlink at all.)

Even toy examples! I'm trying to think back through my recollection of the W3C archives, and I can't remember a single time when a proposed feature had a demo that utilized XML namespaces. Unnamespaced pseudocode, yes. JS polyfills, yes. XML namespaces? Please link me some examples for my fan fiction research.