Now you can export nice DBus interfaces from any source plugin.  Here's a custom "GpsInfo" interface provided by the gpsnmea plugin:

% ambctl
Automotive Message Broker 0.13.800
[ambctl]# get GpsInfo
GpsInfo
{
  "GpsTime": dbus.Double(1050585131.0, variant_level=1), 
  "FixSequence": -1, 
  "Zone": 0, 
  "Fix": 1, 
  "Time": dbus.Double(469297.344, variant_level=1), 
  "RawNmeaSequence": -1, 
  "SattelitesUsed": 0, 
  "SpeedSequence": -1, 
  "SattelitesUsedSequence": -1, 
  "GpsTimeSequence": -1, 
  "RawNmea": "GPRMC,025856.739,V,,,,,0.00,0.00,311214,,,N*48", 
  "Speed": 0
}