I disagree. Times have changed since the original series. Many of the following Trek series (TNG, DS9, and VOY) followed an ensemble format, more or less, throughout their runs. ENT, which tried to emulate TOS with a trio focus, didn't turn out so well. I think modern audiences would be more receptive to an ensemble film, especially in light of successful ensemble pieces like The Avengers and Fast & The Furious.
Plus ensembles would give every character-specific subset of fans something to enjoy in a Trek film.