It's probably one of the most successful examples and a case I had in mind when I wrote my note above. 5-10 million people is quite maneageable in today's terms. I would like even smaller communities, but I'm not a maximalist and this is a size I could compromise about.
Discussion
5m is prob good, 2m maybe better, but of course this is not really applicable to bigger cities which are already much bigger than this.
10m is still a bit too big, you still get several regions with different needs and center-edge disconnects. I'm sure Slovaks would say the same thing, "Bratislava vs the east" etc.
Who knows if it's a good idea anywas? Would it create some very poor countries next to a rich ones just because of some geographic features? Honestly, I don't know even if I like the general idea.