RE: Why is the style tag restricted to the head?

There are several mis-principles being advertised ...

Even to keep a linked reference to a STYLE in the HEAD violates separation of presentation and data.  If you want to be formal, i.e, "pure" about it, all "content" should be in one file, all "style" in another, and a separate "director" file that has links to both the content file and the style file.  The "director" file implies better management of user customization, and also, more dimensions than content and style, such as semantic views, orchestration, translation, etc.  So don't worry, normalization is violated right off the bat.

Also, to say that style or presentation has nothing to do with semantics, is educated inanity.  Just as the inflection of a certain word in a sentence completely transforms the meaning or implication of the sentence, so things such as italics, bolding, even coloring, change the semantics of the document.

HTML, XML, etc., are completely trash, always were and always will be, just like all the browsers trying to chase after it.  It was a typical hack job from average minds, that once started, could never be fixed, no matter by how many committees of egg men, because it was bad from the beginning.  My hat is off to the dung beetles, but an entirely fresh, honest, and correct information architecture is long overdue.  And think of all those schlogs in the field.  Sunken investment is right.

Localization of style is absolutely a good idea, in fact everything should be recursive, hierarchical, and with dynamic adaptive heirarchies -- that would be an internet.