Why would Shatner want to do that?
When it comes to the man who thought a journey to discover god in a series that was never about religion mixed in with a bunch of comedic antics and out of character moments, you can bet that Shatner is the kind of guy who would think more about what's best for his character than what really serves the story, and god forbid, any of the other characters.
It's kind of funny when you look at The Undiscovered Country that the end battle sequence with Chang really does feel like it's missing one important element. Like when Uhura said "Well, what about all that equipment we are carrying to catalogue gaseous anomalies?". But when you think back to the very beginning of the film, it's the Excelsior that was carrying that equipment as said by Sulu himself. So in effect, the Excelsior was supposed to come in and rescue the Enterprise from Chang, but Shatner didn't want to be rescued by Sulu and demanded they change the script, which SFdebris pointed out made no sense since Kirk was rescued from Rura Penthe just a few hours ago!
I wish Nicholas Meyer got around that plot hole, because without having any knowledge of what went on behind the scenes, it makes the writing of the movie feel incredibly lazy.
If you look at the behind the scenes features on the Star Trek II, Shatner is all about "If they did it my way" all the time that when he discusses how Leonard Nimoy kept some secrets from him, he has a big disappointed look on him. I sort of snickered and said "It was for good reason Bill! You'd screw it up!"
One last thing I'd like to bring up about the Sulu footage in the travel pod is the line "I'm delighted. Any chance to go aboard the Enterprise---". Show that shot to anyone, even to a five year old and they'll tell you that Sulu didn't get to finish his line. Just look at him! He's literally moving his head and opening his mouth ready to finish the line, and the film cuts away mid sentence! I seem to recall somewhere that the full line was "Any chance to go aboard the Enterprise is a treat." What was wrong with that?