I'd have watched a Captain Sulu series. But that would have been simply in support of Star Trek, not because Takei has the strength as an actor to carry it. And they'd have needed to surround him with a strong cast.
It would be a disaster for a few reasons:
1. Everyone would expect cameos from Shatner and Nimoy, but if Nimoy was the only one to show up, it would only serve to take viewers out of the plot to think about the Takei-hates-Shatner nonsense. That an absent Shatner would be a distraction on any level would piss Takei off to no end.
2. If the series launched around the time between TWOK - TVH, I doubt Paramount would feel such a strong need to insert him into the films' action (and cut him an additional check), as it would lead to the kind of unnecessary plot / "er--why is he there?"
questions asked several years later when Worf was shoehorned into First Contact.
In this case, the film would be The Voyage Home
, where Sulu finds himself beamed aboard the Bird of Prey (why?) just in time to travel to 20th century earth. Nevermind his Excelsior crew suffering from a total power loss...
3. Knowing Takei's inflated ego, he would request revisiting TOS plots, like the mirror universe, and suggest mirror Sulu is now the Enterprise captain, and the normal Sulu "must" have a face off, thus giving him every chance to chew scenery--with himself--for 50 minutes. Or, I can imagine Takei demanding that plots from the movies (ex. Genesis conflict, or the aforementioned ST IV) find their way on the Sulu show.