The great thing about IE being now a minority browser is that web developers can now say "Oh you want IE6/7/8 support? Oh, that's a minority browser that doesn't support recent things, we can't do that/will charge lots more/etc."
Which means we can finally change from text/html to application/xhtml+xml. This way IE8 and earlier users will get a download message, and you won't have to worry about polyglot/Appendix C anymore.