It's an interesting idea, but I think the problem is going to be that it either becomes predictable, and/or problematic. If you know where the computer comes from or where it would be used, you know the key, and it's not hard to feed fake data in. You're also working with a relatively limited subset of the entropy space (I just made that I up) unless you get really granular on the coordinates, in which case you need a good, reliable signal to make sure the GPS coordinates are stable. You also have the issue of only being able to unencrypt the device at a specific location (i.e. I take my laptop to Starbucks to work and now can't get it to boot), or you have to know the GPS coordinates of where you're going and you have to be able to program in multiple keys.

However, it would be pretty awesome if you combined positional cryptography with traditional, in the sense that you could set a different password based on location. I.e. a 6 character password for at home, 10 for at work, 15 for at Starbucks and a 64 character password for anywhere else.

Part of the resistance towards requiring training is that it provides a means to abridge the 2nd Amendment. It's possible to make it very difficult to acquire a gun by making it very difficult to get the training necessary. Perhaps you only offer it in one location, perhaps you make it expensive, perhaps you only offer the class once a month and have a class size of 20 people. It's how California has basically banned concealed carry.

I think it would make more sense to just make the training universal, integrate it into phys ed in high school or something like that. I don't know that I would integrate actually firing a handgun, but some general information would be good I think. Things like where the bullets would come out, how to check that the magazine is empty/ejected and the chamber is clear, how to safely clean a gun, the kind of things that bullets will penetrate (I hear people thinking that stuff like 2x4s or drywall will stop a bullet sometimes). Just general information that you should know any time you will be handling or near guns. The gun ownership rate in this country is very, very high, I don't think it's imprudent to make sure that the populace knows at least enough to unload a gun and put the safety on.