Xhtml 1.1

For better or worse I have coded all my pages to xhtml1.1 but have to
serve my files as ‘text/html’ because of IE.

Just discovered on the DH wiki (tremendous resource!) that it is
possible to serve my files as ‘application/xhtml+xml’ and use the
.htaccess file to serve appropriate pages by server negotiation.

What I love about xhtml1.1 is that Iceweasel at least is totally
unforgiving on coding errors - browser refuses to display pages that
are being composed if there are any typos or other errors.

Is there any downside to delivering content as 'application/xhtml+xml’
with fall-back to html?

Regards, tomt