He really can't tell the same story. A lot of those surprises were *awesome* when you first get them - like Sheridan being Valen, the Vorlons basically being angels to every alien species folklore, the Vorlons being just as bad as the Shadows, etc. are all things that will have to be written differently.
I also read something that JMS doesn't even want to cast the same characters - its very unlikely he'll get actors of the same quality as the guys in the original; G'Kar and Londo will be very hard to replicate as an example.
I think the premise might remain similar - like order vs chaos, Earth withdrawing from the galactic stage until they need to be liberated somehow (Night Watch, Psi Corps, etc are very applicable in today's society) but the story and characters will all be completely new. I'm optimistic only because if JMS delivered on a good story once before so there's a chance (even on the CW) for it to be good.