I have seen solutions here for the problem, that gpsd grabs the port and one cannot connect to the focuser. These involved shutting down gpsd entirely or disabling auto connect. 
My solutions was to edit /lib/udev/rules.d/60-gpsd.rules and comment line 44, that holds the ID for PLLs USB-serial controller, the same being used in both focusers. This way, the port is not grabbed by gpsd and I am fine as long as I do not use a GPS device with this chip.
From my limited point of view, I do not see any chance to ask the user for intervention, if two different devices use the same chip. At least, in line 34 it says, FTDI rule is disabled, because too many other devices use this.

Any comments?
Thanks a lot.