I think capture now depends on curiosity's GPS filter as a way to get the overlay working. I do agree it should not depend on xPort for GPS data but read the values from a COM port (that can be a port from xPort).
I guess the priority was to get overlay working and depending on GPS filter is not that bad while a better solution is found. Nothing wrong with combining programs together, thats how stuff gets done in linux. If GPSfilter does not interfere with your GPSGate it should work for you