There is much more to HTML5 (or to HTML4 for that matter) than three elements (those are elements, not tags).
You can have your XML with XHTML or HTML5 XML serialization.
Oh, but that does not solve the "flexible" part, right?
Well, you have to choose there — either flexibility or interoparatibility. HTML5 focuses a lot on the latter.
What do you want? To have any arbitrary element in your markup? Ok, you get your <foobar>barbaz</foobar>. And then what? What should it mean to everyone else beside you?
What do you gain by that?
"What do you want? To have any arbitrary element in your markup? Ok, you get your <foobar>barbaz</foobar>"
Yeah I want my own elements that do anything I want, and I'm working on a solution to it. And this project is what led me to the conclusion that beyond adding 3 tags HTML5 really doesn't address any of the bigger issues. I think it's really silly how much hype HTML5 is receiving when it's a patch job at best.
Well, the sooner you have your solution ready, the sooner you will understand that you were solving the wrong problem.
By the way some of the new elements in HTML5 (and there are not three but almost thirty new elements) are in fact supposed to save web developers from the need to invent theri own way to express some common semantics in HTML, e.g. section, artcile, nav, header, footer.
There are alos a buch on new API, much richer inputs collection for forms, etc.
You can have your XML with XHTML or HTML5 XML serialization. Oh, but that does not solve the "flexible" part, right? Well, you have to choose there — either flexibility or interoparatibility. HTML5 focuses a lot on the latter.
What do you want? To have any arbitrary element in your markup? Ok, you get your <foobar>barbaz</foobar>. And then what? What should it mean to everyone else beside you? What do you gain by that?