He think he waited a year too long but he did drop the weight this past year. I feel like if would have worked on changed his game this last season it would have been better, but he can't do everything at once. I am sure if this year continues like it does he will change his game up in the offseason, it would be a must like you said.
Yeah, he should have started a little earlier. MJ and Kobe added little things over the years. First it was working on mid-range shots, then post moves (Kobe even went to Houston one off season and worked with Hakeem on footwork in the post), etc. anything they could think of to stay on top a little longer.
I'd bet that for the rest of his career, we'll see less of Lebron doing movies, appearances, etc. in the off-season and more adding things to his game. One advantage Lebron has with his combination of size and strength is, he can likely add things to his game (especially in the post) that Kobe and MJ couldn't.