There are many people who have complained on the forums that using Heian-era families for Japan is silly and anachronistic. I take the other view. I think it's not silly or anachronistic enough!
Therefore (well, that and because I'm a bit of a fanboy) I have decided to replace the four Heian families with the four Japanese pokemon regions. Isshu/Unova is not yet included, as it's on the other side of the world and I don't know what tech group to put 'em in, and the games aren't even out yet outside Japan.