Keef
OK, DME-DME fixing makes sense, it is the most accurate of ground based navaids anyway. But we then have to buy yet more kit... is there anything for GA which gives a moving map, driven by GPS with a DME-DME fallback? The airliner systems have that I believe. Technically it is trivial to do once you have the map database to start with so you know which DME to ping.
This sort of thing could be done with an add-on DME-DME box; all it has to do is emit an NMEA data stream and one can drive an MFD with that... Fit a switch on the MFD input so it can be fed off either a GPS or a DME-DME.