I think eventually the games will merge. EOC is clearly not a workable system. It needs to be totally remade. It has always been a temporary game, whether anyone will admit that or not. The osrs engine is primitive and just bad. I see many complaints by osrs players of issues that have been fixed in RS3.
So for this game to have any real future they will need to address all these issues with an ultimate version of runescape on the nxt client. And yes, they can find a way to transfer the osrs player achievements onto the new engine.
Don't cry at me though. This would take at least 5 years from now to get done.