There's around 100-150 players in main RSC everyday. There's 3 servers and even that is not enough for certain training activities for there's very few players needed to hog all the world's. Considering the playerbase now and potential playerbase that will be when P2P is released, 2 servers at least is very well needed.
As for those who argue about splitting of community whether in general or PKers, there can be an unofficial world for PKing and community meetings/trading. I'll put main RSC as a prime example. When people want to trade/socialize/meet the community, they will mostly gather in world 2 draynor village. That goes for dueling(often) and PKing too(if there's PKing). Is it set in stone that world 2 dray is a place where people meet? Hell no. The community set this up and due to the fact many people follow this "unofficial custom", it attracts more and more people, old or new, to actually clog W2 dray for those purposes.
If the pkers/skillers here set an unofficial place to trade/socialize/pk in unison, the good number of people that agreed to follow this "unofficial custom" will attract more people to follow it and therefore create a norm. Those who just wanna skill/train can go to the other world as when one world unofficially becomes a socializing/pking/trading world, the other world automatically and unofficially become a training/skilling world although both worlds can be trained on.
The problem of community splitting shouldn't be an issue. I was a main RSC player and an active one at it too(member of The Guardians), I know community splitting issue is a non-issue even in the game where there's more than 1 server and more or less around this number of online players and especially when P2P is released.
EDIT: My opinion and suggestion? Give 2 worlds. All unite and agree on a world and place for PKing and socializing, trading, etc and try your best to enforce it so that others will know where to go for socializing/trading/pking/whatever activities. Try to encourage trades/businesses to be conducted at that location. That way, there's no problem with splitting the community, pker, traders, or skillers.
It may be a little difficult at first, but once people are past that stage, there is no problem anymore. Anyone who plays OSRS will know Varrock West Bank is where, I dare claim, 90% of the trades take place. Yup, I play that game too.