Actually, while the default chat being /local might stop the new guys from being exposed to some RP, it will also stop them from being exposed to mass spams of ooRP chatter, that is very likely to happen in any highly populated system.
I believe that with a local default instead of systemwide transmissions, it will actually help with stopping the ammount of out of role play people, as they will be more exposed to inRP messages, from pirates, for instance, which would gradually, over time, lead to a better percentage of inRP communication over ooRP. Which would, of course, be a good thing.
So, long story short: My vote goes to /local being default with optional systemwide switch, like Jinx proposed, only backwards
