OK, regarding the original issue of using maps unlocked to a 10x or 20x with the software-only version of Mobile PC, I have had an extensive interaction with Garmin Technical Support, and they said that they would refer it to Software Development.
Whether this leads to anything is difficult to say.
The solution is actually simple - just modify the software so that the software Unit ID is still used as at present (for people using non-Garmin receivers) for the maps that come with the software, but if a Garmin receiver such as the 10x or 20x is used, then it must also allow maps to be used that are unlocked to that receiver (as in the case of Garmin Mobile PC if the product is purchased with the 10x (010-00742-00) or 20x (010-00685-00)).
Now let's wait and see what happens.