While having DS9's Sisko would have been a great crossover, having two captains on board would have overpowered the film...not to mention in the end it's Picard's ship, and he has seniority. Supposedly however a Sisko ordering Worf scene was filmed; I'm glad it was cut as it hurts the pacing.
But I like Terry Farrell's suggestion that she could've been at the Defiant's helm.
And speaking of Lily and Picard, I think that it was still more powerful to have them fight it out verbally than Crusher vs. Picard (shades of the Pasteur argument in AGT---good for that ep; in FC they needed an outsider to yell at Picard). However it was a missed opportunity to not use Crusher more somehow.
Also as mentioned in another thread, the line "I never read it" by Lily supposedly implies lesser traditional Western education on Lily's part, allowing Picard to play the more 'civilized' angle. Maybe if Lily had read Moby Dick, and they could have continued the discussion similarly, even explaining Moby Dick to the audience despite both having read it. Maybe Lily could have read it..."a long time ago"...
Which brings me to good opportunities in FC. The way they explained things in techno/lay terms was quite skillful ("temporal vortex"/"time travel" etc.) helped the pacing IMO.
