I love the whole idea of a show about Sulu on the Excelsior. It's always been my guess that Takei took a reduced role in Undiscovered Country specifically so that he could establish Sulu on the Excelsior and open up the possibility for another series--though I'm sure someone'll correct me if I'm wrong.
Comments about George Takei aside, though, some of the critiques here seem to be about how the Star Trek franchise had fallen into misguided hands at the time, which meant that any Trek produced at the time would have been troubled (as it was), and not that Sulu himself couldn't have carried a series.