The following concepts listed above have been explored in the trilogies and short stories:
Aftermath of Centauri conflict and rise of Vir Cotto:
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black> Dealt with in Centauri Prime trilogy, and the bulk of the building up and subsequent action occurs years later, nearer to Sleeping in Light on the timeline. I don't remember the Rangers appearing in it because Vir avoided help from outsiders except for the mages. But there's no reason Vir couldn't show up once in a while. </font></td></tr></table>
Valen flashbacks:
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black> The last DC Comics miniseries "In Valen's Name" had a lot of this, including a major revelation regarding Sakai. </font></td></tr></table>
On TV it would be difficult because of the need to get
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black> Michael O'Hare (does anyone really not know he was Valen? Come on, it's revealed in the first five minutes of The Gathering, though it wasn't originally.) </font></td></tr></table>
back. Judging from his IMDB entry, he retired following his last appearance on B5. Then again, Andreas Katsulas retired after B5 wrapped too.
As a side note, about chrysalises (chrysales? chrysali?):
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black> We know Delenn's chrysalis was made using Vorlon technology. Mage chrysalises derive from Shadow technology. Is there any connection between the two other than the name? </font></td></tr></table>
Lyta's life following B5 was touched upon a very little bit in one of the stories Joe did for Amazing Stories before it went under, a neat Lyta/G'Kar travelogue kind of thing. I think it was called Genius Loci or Genus Loci. Standalone, no spoilers per se, but at least you get a feel for where her head was at between the events of the fifth season and the teep war. One of the stories in the British B5 magazine dealt with more arc-related events involving Lyta and Garibaldi, but still seems to be just barely pre-teep-war from the descriptions I've seen. Of course,
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black> Lyta was supposed to appear in one episode of Crusade as well, so it isn't a given that she couldn't still be alive after all. </font></td></tr></table>
Ivanova's life post-Season-4:
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black> The short story Hidden Agendas, which only appeared in the British B5 magazine, has Ivanova returning to B5 in early Season 5. Her appearance ties in ominously with some of the stuff dealt with in the unproduced Crusade episodes and the mage trilogy. A neat (or creepy) coda to her life is depicted in the Marcus story below.</font></td></tr></table>
Marcus:
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black> Dealt with ultimately in the short story "Space Time and the Incurable Romantic", also from Amazing Stories. This is one of those "set the cat among the pigeons" stories according to Joe, and I agree. It is kind of a bummer to find that he was never resuscitated within the B5 timeline, but a very romantic (or again, creepy) resolution to his relationship with Susan. </font></td></tr></table>
Really, here are the unresolved threads I can see from what's already out there which could be addressed in the 2265 timeframe (just sticking to main characters in the show and novels):
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black>
What happened to Bester during the gap between the second and third teep novels?
Are the mages really doomed to extinction?
To what extent is Earthforce still beholden to Shadow interests?
How did Sakai come to be sent back in time to see Sinclair/Valen? (But I assume this took place behind the scenes prior to Into the Fire.)
Does Zack EVER get laid? (Um, never mind...)
Whatever happened to Lennier? (He's sometimes referred to as having died during the teep war, sometimes not. Being that he was pretty connected with the Rangers, though...)
Did the Vorlons have minions like the Drakh were to the Shadows? (just me wondering, it never came up during the series AFAIK)
What is an apocalypse box and who has one before Gideon?
What were the Drakh up to between the events of The Fall of Centauri Prime and A Call to Arms?
What is WITH Lochley, already? (Er, sorry...)
</font></td></tr></table>
And of course the threads that become available after the pilot airs, involving this new race we never hear about in flash forward episodes, and the politics of Rangers.
I know this seems a little obsessive, but it's a tribute to Joe's eye for continuity that there are so few threads to pick at.
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