^Not really feasible in this case since while the live action footage was shot in widescreen, the CG was rendered in 4:3. Even if they tried doing a cleaned up version of the show in 4:3, given the relatively low resolution and video based format of the original renders, it'd look horrible in HD and no amount of filters or messing with the colour sliders will improve matters.
It's been said by many people who should know that the *only* way to get a BluRay release for B5 is to totally redo *all* of the CG shots. That's everything from space scenes, to PPG blasts, creatures, planetscapes and graphics. It's also why it'll only ever happen if WB can be convinced that there's a significant enough market to invest a *lot* of money into the product.