My XML5 idea is over twelve years old now. I still like it as web developers keep running into problems with
tdelement. There is also no way to create a custom element that contains certain HTML elements, such as the
trelement. (See webcomponents #113 for more.)
ShadowRootnodes to enable server-side rendering. (See dom #510 for more.)
XML in browsers has much less of a compatibility footprint. Coupled with XML not always returning a tree for a given byte stream making backwards compatible (in the sense that old well-formed documents parse the same way) extensions to it is possible. There is a chance for it to ossify like
text/html though, so perhaps XML5 ought to be amended somewhat to leave room for future changes.
(Another alternative is a new kind of format to express node trees, but then we have at least three problems.)