Modern web site design with XML and XSLT

You can't find a book with that title. Some naive questions. I'd like to
take an ecommerce online application I've written and convert all its
drop-down, CSS, blinking lights, Ajaxy goodness to all XML/XSLT all the
time but, as I have just started tinkering with this, I run into
articles about how browsers of today don't support XSLT or it won't work
with HTML5 and all those other things that make one question whether the
effort is worth it. I think XML is ideal and I don't know why I couldn't
convert everything over.

I need either encouragement or discouragement that my (unknown to you)
web site that uses bleeding edge modern web development techniques
(CSS3, HTML5, Ajax/Javascript/DOM, etc., works in all browsers) can be
completely recreated without worry of gotchas halfway through the
process. That something won't ever be supported so I'm stuck and all
that.