i guess that makes sense. I personally find it excellent and flexible, especially with the php function calls you can do from within it. although I imagine it wouldnt be possible in EE, because it would be a fundamental change in the output engine, it would be nice to have the option to do templates in xsl. not gonna happen tho.
I think templating with XSL, though powerful, would limit the audience and consumer base for ExpressionEngine. Even though it can be learned, it wouldn’t appeal to many. Why learn a new language to use ExpressionEngine, when there are other CMS systems (free ones no less) where I only need to know HTML and CSS (if that).
Right now, all one needs to know is HTML and CSS. This means that everyone on my team can alter templates. In the past, I was stuck doing a lot of the back-end templating changes as the main developer for my firm. So, the entry level is for a non-developer. Using XSL would raise it to more technical people.
That might be the fundamental reason why it’s not implemented—not only in EE, but in other CMS apps as well.