A reporter from a brazilian website interviewed Bruce Boxleitner at the Comic-Con about TronLegacy, on july 24, and he told that he had spoke with JMS the day earlier, and that JMS told him that he already has an idea for a new B5 movie. I will translate what was posted on the site:
"I (BB) spoke with J. Michael Stracynzki and he mentioned an idea for a new B5 movie. I thought that the concept is very interesting and it would be fantastic to contribute again to the B5 universe."
On another site, quoting the same interview:
"We spoke about this yesterday and a new movie is finally going to happen. It would be great to work again in this franchise."
I don't know what where the exact words said by Bruce, because I'm translating something that was translated to portuguese in first place, but still I thought I should share this.
The links to the sites where I found this (portuguese):
http://cinema.terra.com.br/comiccon...rsa+com+atores+e+equipe+de+Tron+o+Legado.html
http://www.soshollywood.com.br/babylon-5-pode-ganhar-novo-filme/