I stumbled across something interesting. A few years ago JMS released released a volume set of his shooting scripts for every B5 episode he wrote. Each volume also included concept art and notes by him. The final volume was his origional 5 year plan for the series. It contains an outline that JMS wrote in the year between "The Gathering" & "Midnight on the Firing Line." Unfortunately I don't have the book as the only way to get it was to get all of the other books in the series, sort of like how Time Life releases book series, and the whole thing is out of print.

*****MAJOR SPOILERS AHEAD*****

Another fan was nice enough to put together a summary of it & it is, most interesting.

On more general notes even though JMS has often said that B5 was a story with a beginning, middle & end and that he had no desire to become a "deep space franchise" this is just not the case. Aside from him having 2 failed attempts at launching followup series ("Crusade" & "Legend of the Rangers") his origional outline ended the series on somewhat of a cliffhanger and than had a rough outline for a followup series called "Babylon Prime." Of course JMS has engaged in Soviet-style revisionism before after changing his mind on something. What a shock; the creator of B5 likes to make up stories. The interesting thing is that lots of elements were planned out, in some form or another, like we saw them on the series. While others were changed, dropped or don't appear at all.

Notably absent is Sinclair becoming Valen and taking B4 into the past. In this version it was prophesied that Sinclair would save the Minbari from extinction. Delenn still undergoes her transformation, marries Sinclair (who would have stayed with the series the whole run) and they have a son. Here's where it gets interesting.

The breaking of the Grey Council we saw in the series was instead going to be the warrior cast overthrowing the Council in season 5 and resuming hostilities against Earth. The origional plan was for the series to end with the destruction of B5 at the hands of the Minbari fleet. Delenn & Sinclair would escape with their new born son, David. They would be wanted by both Earth-Gov & the Minbari. All of this would be a setup for a follow-up series Babylon Prime.

Babylon Prime would pick up just where B5 ended and feature Sinclair, Delenn & their allies going back in time to steal B4, as depicted in Season 1's "Babylon Squared." The older Sinclair we saw at the end of "Babylon Squared" would have still represented and effect of the time travel; the time travel would also have the effect of speeding David's aging so that he grows to adulthood in just a few years.

Station Babylon 4, would be renamed Babylon Prime and be the new base of operations for our, now renegade, heroes. B4 was established to be bigger than B5 (B5 was built on a shoestring budget after B4 disappeared) and would also have engines that allow it to move from place to place like a starship. "Babylon Prime" would involve our heroes trying to build an alliance, clear their names. Emperor Londo's keeper and the Centari's conquest of other worlds would feature as well. B-Prime would end with Londo making a sacrifice to help our heroes escape; presumably as seen in the flash forward of "War Without End" and foretold in his death dream. The militant Minbari would be defeated, David would become a revered religious figure to the Minbari and the head of the Installer Alliance.

JMS is fond of saying that no plan survives the first encounter with the enemy and his big plan for B5 is no exception. When they started Season 1 he was very quickly told that if ratings weren't at a certain point by the end of the season they were not getting a second season. Indeed the show was on the verge of cancellation each and every season. I'd imagine it was at that point when JMS realized that saving some of his best stuff (breaking away from Earth, the resolution of what happened to B4, the formation of the alliance) for some pipe-dream followup series wasn't a good idea and he started using it in the main B5 story arc.

Some of his other ideas, the characters going from place to place looking for something was reused in Crusade. And if crusade had continued the crew would have become renegades from the Alliance for some period of time.

Interesting. The planned storyline seems to have changed as time progressed. I'm sure I read somewhere (long ago) that there was always going to be a Sheridan character brought into the series and that he was only brought to the fore when Michael O'Hare left, but there's no mention of him in the link above.

It was rather brave (or arrogant?) of JMS to be confident that the Babylon 5 series would be so popular that it would warrant the spinoff Babylon Prime series.

I'd heard JMS has claimed that there was going to be a Sheridan-type character all the time. Of course JMS has been known to contradict himself in the past when making claims about the series; much like George Lucas when talking about changed premises in Star Wars "no, no I planned it that way from the beginning."

Also this rough outline was written between "The Gathering" and "Midnight....". There's no mention of the doctor, first officer or telepath; probably because JMS knew the origional actors weren't returning & hadn't worked out the who's & hows of their replacements. I'm sure that by the midpoint of season 1 he was already rewriting the thing.

And you are correct on the wishful thinking of saving some of his best stuff for a spinoff/sequel-series 5 years later. I'm sure that's why he decided to send b4 to the past and cover most of that ground in the 5 years.