Warner Bros. hasn't said a word about any of this.
My guess:
We won't see any more "double feature" discs. Warner Bros. did that because they needed a "test disc" that was self-contained, would prove a fair test of the popularity of the series, and would have some hope of selling to non-fans who had heard of the show but weren't familiar with it.
But there were problems with the available material:
TG isn't, even in its re-edited form, a terrifically good movie. It is trying to do too many things at once, and is overstuffed with plot and backstory. It is also too far removed from the series in terms of cast, "look and feel", props, makeup, etc.
In the Beginning is a better film, but it highlights the S2-S4 cast, and doesn't feature the station or the situation at the time of S1 - which would obviously be the first one released if the test disc sold well. OTOH
ItB, with its flashback structure, gives a sense of the scope of the epic, without (contrary to what some critics have said) actually giving away very much of the plot. In typical JMS style the movie shows us that certain events have happened, but doesn't give us the
context, doesn't tell us
how they happened, which is what we really want.
By releasing the pair as a two-sided disc Warner Bros. controlled costs, made the disc a real value to attract impulse buyers, kept the releases in "chronological" order within the story, and offered both fans and new viewers an excellent "sampler" of the series without issuing some kind of "best of" disc.
Given the success of the first two seasons, I don't think that Warner Bros. decision on future TV movie releases will be affected by similar considerations. The
purpose of releasing the later TV movies is different than that of the first disc, and the studio should have no doubt that the later TV movies could sell very well on their own. (Some folks might skip
River of Souls, but I'm reasonably sure that
all of the
B5 TV movies could be released as individual discs at a profit for the studio.)
Of course they might also prefer to release all of the TV movies in a boxed set. The one thing you can be pretty sure
won't happen is their sticking
Thirdspace into the S4 set. The movies have always been treated as separate entities by the studio, and for good reason.
Thirdspace falls between "The Illusion of Truth" and "Atonement". You can always watch it between season discs once everything is released. (As it happens "Illusion" will be the last episode on S4 disc 2, and "Atonement" the first episode on disc 3, so there is a natural break-point there.
)
Regards,
Joe