XHTML 2.0 is the newest version of XHTML. Many unnesscary features of XHTML will be removed in favor of new elements and attributes. XML features, such as XForms and XFrames, will be used in place of the Frames and Forms of HTML. XHTML will remove the <b>, <i>, and <tt> elements so developers will have to use CSS instead.
XHTML 2.0 will require the application/xhtml+xml mime type and will not be avalible with the text/html mime type. The text/html mime type will still be a valid mime type of course, but unlike XHTML 1.x, XHTML 2.0 will require it. On this website, for example, the application/xhtml+xml mime type is used even though it is not required (at the time of writting this http://asolis.net/ is using XHTML 1.1).
An XHTML 2.0 document must have the xsi:schemaLocation, xmlns:xsi, xmlns, and the xml:lang attributes for its <html>. Here is an example of an XHTML 2.0 Document:
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 2.0//EN" "TBD"><htmlxmlns="http://www.w3.org/2002/06/xhtml2" xml:lang="en" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3.org/2002/06/xhtml2 TBD"><head><title>Virtual Library</title></head><body><p>Moved to<ahref="http://vlib.org/">vlib.org</a>.</p></body></html>