Seems to be have gotten a bit too indepth here, on swing speeds.
Player retention is the most important aspect of community growth - that is, a new player who stays.
Some more concrete way this could be done for the weaker NA community would be to lessen GK's stranglehold on the "market" of new players. If I were a new player and American, and I tried to join servers, I would get the impression that multiplayer on Warband begins and ends with siege mode and deathmatch, and that the stagnant GK clan were the only clan in the world.
GK could change the siege server cap to 150, so that at busy hours, a large portion of its players will be shuffled into a new server, GK Battle (?), something most noobs never really play because the battle mode is dominated by veterans. It would appeal to me as a noob who mostly would've had experience with CoD or CS:S, where "battle" mode is the standard.
Would take effort. Another much easier thing to do would be to lower the swing speed to medium and change starter gold to 1,000. remove Khergits as a playable faction in most cases, remove GK embargo on other clans advertising for the community sake (I mean, isn't GK big enough at this point?), and change the map list on the deathmatch and TDM servers to greatly lessen the amount of cavalry and open maps on the rotation.
So basically, copy Europe. Fidilus Unum Erabus.
All of this could translate to using resuscitation techniques on an already dead corpse. A couple of people have said that Americans just aren't as interested in sword-and-board. I notice the NW NA community is actually quite big and healthy, which certainly lends argument there.