Regardless of adoption, XHTML is not being advanced anymore (there is no team working on it anymore). HTML 5 is the way to go moving forward. While still in the works, since it is backwards compatible there's no reason to not start using the doctype now
(and add in functionality as it gets more broadly adopted).
Razor will have intellisense in VS. Also, MVC will have a Razor view engine in the next version.
Yup. Two urls isn't a good idea. Theming can be done independently of urls and having two isn't good for Google/Bing juice (and just doesn't make sense in general). Not saying it WILL be done, just saying it could.