Where are the characters?
*snicker*
Would the tone be like the series, slightly different like the TOS/TNG movies, or vastly different like PIC?
Definitely different, maybe akin to TOS TV/TOS movies - more expansive and a lot more character driven, yet not forgetting what made them work in the first place (for the most part).
The TNG movies did not do well in taking the TNG crew and plopping them into generic big movie
action action action! At best they felt like cast reunion shindigs put on film. Except "Generations", which had more potential - a lot more if 1701-B with Kirk wasn't shoehorned in, which only made more questions needlessly than anything else. Just imagine if Kirk's final movie had a villain that was an overly contrived and botched clone of Kirk himself... (Marta shapeshifting into him doesn't count because she's just working for someone else and uses his visage to not excessively humorous effect, while confusing McCoy with regarding who the real McCoy was, so to speak... Nicholas Meyer taking the time to sit through all of TOS and decide how to retain what made it work while building on it in positive ways, despite not being a fan of the show to begin with, did absolute marvels.)
So with the history lesson done and reeling back in to VOY, VOY was the Trek that was the most similar to TOS TV; anthology or standalone episodes, just with veneers of running arcs at times and characters that could easily be adapted to the big screen. (VOY being standalone was in part possibly because DS9, at the time, dove into serialized storytelling and being ahead of its time, with VOY returning back to the classic mindset.)
So that said... they arguably could take the cast where they left off and do a big movie. The big issue is selling it to an audience, as VOY was more niche than every Trek preceding it. (Jayson1 made a good point and I'm glad I scrolled up before clicking 'post' as I don't always do that but
SQUIRREL! aside...) The second big issue is whether or not to keep continuity with PIC. That's a separate discussion entirely...