Issues with the simulator playback of GPX data.

I have just discovered the ability to playback a GPX file that was introduced but not announced ("Add support for new FIT simulation and playback dialog.") in Beta 4.1.0

This is a very valuable feature for me, and with a bit of tweaking, I have made it work.

There are a few issues.

1. It fails to copy the chosen GPX file into the folder /var/folders/ly/qnh242bx7z98fz51w0yvjvjm0000gn/T/GARMIN because GARMIN does not exist in ..../T/. When manually created, it proceeds OK.
2. position.Info.speed always reports 0.00 This is a bug. (unable to post screenshot) :
   

   positionInfo
   Lang.Object
   accuracy: 4 (Lang.Number)
   altitude: -499.99445 (Lang.Float)
   heading: -0.77554625 (Lang.Float)
   position: Lang.Object
   speed: 0.0 (Lang.Float)
   when: Lang.Object
   

   
   
3. The timestamps, which are mandatory in GPX<trkpt> syntax, are ignored, so the playback occurs in real-time, not those in the GPX file.
4. (the altitude is reporting -499.99.. , but since I'm sailing I don't care about altitude!)
5. It would be immensely valuable if the speed of the replay could be controlled from the playback dialog.