Maybe the swarm of the day/week/month etc.. would be based on what the average temperature is on that day. I live in australia, and If Australia gets an average on 35 degrees celcius (95 Farenheit) maybe a fire type pokemon would appear? That would be really fun feature because then you could introduce country specific pokemon and if you live in a really cold area (North Pole for example) then the only way to get the fire type pokemon that are only available in swarms will be to use the trading by wifi. And vice-verca. If Vanillish comes to this game by swarm only, maybe it would only be available in 10 degree celcius (50 farenheit) weather and since that usually doesn't happen here in Australia and if I don't have any Generation V games (I actually do, but lets pretend we don't) then the only way to get Vanillish into my game would by to trade with someone from the North Pole over wifi.