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?