Default country by user Time zone

I doubt very much you would use or need rules to do this.

It does seem like an interesting idea, but currently would be rather impractical. For example, how would you handle UTC? Ignore it? Or set it to the United Kingdom? Aside from that, we'd also need to figure out how to map the timezone names to the actual country codes. This would probably need to be a giant array, and not something I'd really want to look at at the moment.

Patches to add this functionality are welcome.

I don't think this is possible to do in an automated fashion, actually. GMT-7, for example, encompasses a wide range of countries from Canada down to the bottom of South America.