Although we have an (unused) SPDIF output on the board, I'm not aware of there being an input. Either way, you're talking about a major hardware revision, and we only just finished Mk.2 (which is actually Rev.7).
A much more likely solution is to utilise the Aux line inputs and the serial port in conjunction with an adapter box. We know how to talk to (some) CD changers because we've already done it for an OEM (albeit the other way around) however there would be some considerable development overhead and we're pretty much tied up for the foreseeable future.
Controlling an autochanger also conflicts with our marketing approach, although I think it would be a reasonably worthwhile future tick-list feature. Speaking personally, the only time I miss a CD head is on the drive home from the music store after getting some new discs!
Rob