I want to know what the story is with Justin, who he was, how he came to be Sheridan's opposite number and how he ended up on Z'ha'dum because he definitely wasn't onboard the Icarus.
I think the rational behind the Mars scenes looking like they're at 1G (other than the fact that they are) is that if you live on Mars you adjust to the new gravity and over time you relearn how to walk in the lower gravity well. Oh and just for the sake of being a smart arse, Mars gravity isn't 0.25, I think it's more like 0.38.
As for the Vorlon Homeworld, it was obviously closed off because like Z'ha'dum it's full of scary dangerous crap that could do untold damage if a bunch of unevolved apes start poking around and pushing buttons. So I think the Vorlons effectivly put a time lock on the place that would seal off Vorlon space until the surviving younger races are responsible enough to understand how to use it.
I do wonder though, if JMS actually had an idea for a story that far in the future. I wonder because when Ironheart goes all christmas-tree-man in Mind War, he says he'll see Sinclair again in a million years and there's the thing about Valen disappearing, much like the way SHeridan disappeared AND Delenn having a vision of Valen (who called her one of his children) when she was little. In a nutshell, I think Jeff is still around.
Small aside about the Delenn's vision; I wonder if that's what was going through Delenn's mind in "Soul Hunter" when she's half delirious from blood loss and actually recognisies Sinclair as the Valen from her vision. "we were right, about you."
Oh, interesting little Crusade tidbit for those who didn't read the unshot Crusade scripts (I'll try not to spoil too much) but I think there was mention made that the Excalibur was to have an "opposite number". That is a ship out there with the same Vorlon "death beam", possibly working for that Earthforce Bio-Weapons division that's been behind a surprising amount of shenanigans since B5 season 1. I wonder if there was going to be a Shadow Hybrid Victory at some point. That would have been fun...in a cheesy knight rider/Karr kind of way.