People have been making really good points here. I'd like us to put in a new player's shoes and try to think what we would do if we were joining RO2..
Let's say we already know about dungeons being really hard to solo, so we'll obviously want a party. Will we actually choose the fresh, new, empty, server that might have very few people and so it would make it harder to find a party? I think we'd rather stick to the server with highest population. At least we have almost a certainty that a veteran player might be around to give a hand.
I honestly can only see old players trying the new server for fun, making a new char and all that. But some others will find it boring, specially if you don't have any interesting stuff in the AH to make the whole grinding late game a bit more meaningful (In my case, I only wanted to grind up to mukas to farm zenny and buy stuff from the AH). I can see people quitting if they're unlucky enough to login at certain times when there are few players around, getting bored to death while sitting around dungeon entrances.
Giving a new server with the same exact build is a stupid move, ODIN isn't even over-populated so there wasn't a need to split the playerbase. If they had made a server with new (or old, but wanted content) everyone would be happy about it, but that's not the case here. So I wonder if this will actually work or not, my feeling is that it won't.
@Fluidz, afaik, the account is the same so you can just choose Freyja instead of Odin and play with your Freyja chars, but you can't login to both at the same time, since dual client isn't allowed. And you can't even login in two different computers using the same account.