Like I said it's PDOP that's being measured anyway, it's unlikely to be changed from people referring to it as HDOP as that was the value that was the original intent.
https://github.com/diydrones/ardupilot/issues/462
....
http://data:image/png;base64,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
The uBlox NEO-M8N was tested alongside the NEO-7N by 3DR (in the US, EU and Australia) and it didn't pass their testing, the wideband antenna for one picking up more noise so the true results between the two were negligible, this has been dealt with on the Solo Facebook page a number of times. The M8N also reports satellites in the count it can't usefully utilise which artificially lowers the HDOP (and potentially PDOP) it reports so it can allow a take off when strictly it shouldn't. Finally there's also an open bug using the M8N... So in a nutshell it's a wasted modding effort right now.
https://github.com/diydrones/ardupilot/issues/2097