Everything that you want to do, is possible, and those of us who can help, will help point you in the direction you need to go. Feel free to stop by #linuxmce-devel on freenode IRC.
You will need to study DCE devices, how they work, and build your own simple DCE device (see Developing a DCE device), so you can understand the interaction.
Once this is done, you'll need to study the interaction of Plugins with the DCE router, as you'll need to understand this, for handling the MediaStream object and its friends.
Once you understand this, you can then look at the MythTV Player, and see how it interacts with the existing mythTV, you can choose to keep this mechanism, or embed libMyth into MythTV Player (in actuality, the first version of MythTV literally embedded libmyth directly.)
Do you have the patience?
I'm familiar with the DCE router and how it works. I spent many hours (and a lot of money) on LinuxMCE back when it was first starting out, and got a good amount of experience in that. I would have needed to study up on the plugins though. I'm also fairly familiar with mythfrontend, namely with theming and remote control. When I was still considering this project I was thinking that the majority of the work would be in the theme.
This certainly would have been a large project and taken the majority of time for a while, but I was ready for it... wouldn't be the first nor the last large dev project I took on.
BUT, after getting that initial response, I started remembering why I left the LinuxMCE community years ago. I then did a search to get up to speed with the recent events of LinuxMCE... and found Hari even started his own system, because he got so fed up. That put the final nail in the coffin for me. I haven't even thought to rechecked this post until now... just because I can't sleep and got curious.
LinuxMCE is a wonderful concept, but led by some close minded and rude developers. That just makes for an environment that I don't particularly want to work in... especially for free. I'm not aiming that at you, Thom; you've done a lot for LinuxMCE, and it's users, when I was around; and likely have continued to do so.
Of course, like Hari, I still need a Smart Home Automation system. If anyone's interested, I'm currently donating my dev time to Pytomation. But there are a lot of home automation systems out there. I'm still considering Home Genie (looks like some Pluto devs made that), but I like how easy Pytomation made it to create new interfaces and devices, and add custom code.