You will need to have Asterisk on you Core, but you can copy your config files over and use them directly. I did that once and then I decided to use the LinuxMCE standard way as LinuxMCE keeps a lot of configuration inforation in its databases that it needs to do some of the cooler things. This was a disruiption in service, but it's the best way really.
Yeah, this is definitely an option. A couple of days of service interruption is not a big deal. I was more worried about extended instability. My only concern is that the version of Asterisk in Ubuntu Feisty is the old 1.2.x series, and the one I am currently using is 1.4.x from Debian unstable. Asterisk configuration files are not backward-compatible so I'd need to redo my Asterisk config. (and I spent some time fixing some things in the 1.2 to 1.4 migration.)
Ubuntu Gutsy does have Asterisk 1.4.x. Guess one option is to try APT pinning to get Asterisk 1.4.x after doing the LinuxMCE initial install.
As for MythTV... I wish... This is actually a big problem for me. It seems LinuxMCE uses an outdated version of MythTV and is incompatible with the newer releases. However, if your backend is the same version then you can use your existing Myth system. Although you should move the database to the Core.
Indeed, this is a big problem.
I almost forgot... the Kubuntu thing is being discussed in the Developer forum. I still don't understand it's rational...
Oh, cool. I'll check it out; thanks for the info.