Having played (and enjoyed) DAoC I think you are being overly pessimistic. Ignoring the fact that an enormous shared dungeon to fight over is actually really fun (danarchy touches on why a few posts down), I believe that it will actually make the RvR fights even better. People who typically are only interested in PvEing will finally enter RvR in order to open up the mega dungeon.

The only worry I'd have is that one thing that made Darkness Falls great was the tug-of-war between the three realms to keep it open. I wonder how well this will translate to two realms, and I wonder how they intend to balance it so that a server with a dominant population on one side or the other does not end up with the new dungeon 90% of the time.