There has been sporadic talk about using a SheevaPlug as a master backend for MythTV. I was under the impression that nobody had attempted to do this. I was wrong.

The verdict: if you want the SheevaPlug to do serious backend work you will probably be disappointed. However, if you want to have a device that is low power and can wake up a slave backend then this is ideal.

It seems the real challenge is that currently the MythTV (0.22) codebase does not support a master backend configuration that has no tuner. This can be worked around by using a round-robin scheme or by using a fake (or development) tuner on the master backend (see also here).