It's a bit difficult to understand how there could be a shortage of ST:FC style uniforms there, as the scene doesn't really include more people than there were in average ST:FC scenes, and the suits on those "TotP" background people wouldn't have to be exact fits but could be randomly sized examples on randomly chosen extras... But perhaps it was a matter of a badly chosen laundry day at the studios?
It's in any case a cool idea that many of the ships and their skippers at that point of the war would still be newcomers, units rushing back from deep space assignments.
As for officers choosing their own garb, I very much like the idea that the TNG and DS9 styles were all part of the same uniform "generation", and were interchangeable "Class A" and "Class B" versions. However, I'd like to see the ST:FC style as an all-new generation, perhaps the "Class A" variant of that generation but perhaps instead the "Class B".
It would be the very high-ranking people, basically the Admirals, who would get to wear uniforms that aren't exactly uniform. Eccentric old bastards playing fast and loose with regulations would nicely explain the great variety of styles during the early TNG seasons, or the very off-standard looks of the fake Admiral Janeway in "Coda", or the fact that a ST:FC-style flag uniform appeared on DS9's Admiral Ross much later than did the line officer and crew ST:FC uniforms on Sisko and pals.
Timo Saloniemi