Well, there is kind of a roadmap at http://svn.charonmedia.org/trac.cgi/roadmap
From my knowledge, the roadmap is like this:
The first issue is getting LinuxMCE build from scratch.
Hava a first comunity-release. (planned 0804)
Besides that, I consider Bugfixing and making existing functionality work is a major priority. That includes the secure private files with pin, mythtv-issues, and so on.
After that, I guess the developers willing to contribute will be the ones defining priorities. So feature wishes that come with an implementation are likely to be included first.
Besides that we will need maintainers for the different areas of linuxmce and master-maintainer, and stuff like that.
So my guess is that before a "real" feature-roadmap can be defined, we will need to do the base working first and then it depends on the developers choices.
You are welcome to contribute and work with the rest of us.
Best regards, Andreas