I suppose if other people more ideas post them here.

Regarding my ideas for a (what I like to call) "Northern Empire" border mod would be editing the river borders of the major rivers of northern Europe, such as the Elbe (Germany), Vistula (Poland, Daugava (Latvia/Russia) and the Volga (Russia) so that no counties are split between them.

On top of this, switching around baronies so they appear on the same side of minor rivers in the northern european greater area, counties to which this would apply in this region would for would be for example: c_brandenburg, c_berlin, c_landberg, c_poznanska, c_zakroczymska (this particular county is even weirder as the barony of b_wyszkow is itself spilt in half by a minor river), c_trakai and c_kernave.

There are doubtless more in the general area of these places I described (though I think I got all the major/important ones), but going after the feel of a similar empire forming in the Baltic Sea region they doubtlessly would expand along natural borders (rivers, mostly, in this region) just as the Roman Empire. The follow up from adding more natural borders is that you'll also be recreating possible/alt-history borders for the Roman Empire, lets not forget that the Romans attempted to push their borders all the way to the Elbe and any Emperor who wanted to "one up" the guy who just restored the Empire would want to do what the Romans of old failed to. Any work putting to making more natural borders goes in both directions, be it a Roman Empire of not.