Complaining about whatwg's URLs specified in a 18-page informal procedural description compared to RFC BNF? How about whatwg's HTML5 being described in 100's of pages rather than SGML DTDs or other formal language?
That approach was tried, was called XHTML, and failed because it turns out that backwards compatibility with existing content, and with previous implementers' dubious choices about how to interpret that content, is not actually optional. HTML5 is complicated because it has to capture a lot of behaviors that were never designed to be a spec that people would code against.
Nope, they didn't even try, and have absolutely no idea about SGML. Hixie just wrote the initial HTML5 spec out of his ass, and it's been fossilizing since, with major errors. XHTML has nothing to do with it.