LeBron is entering year 17 of his career. Add the 8 straight finals appearances plus all of the other playoff mileage of his career and he has played the equivalent of 20+ seasons. He will be 35 on New Years eve.
Kobe Bryant, who had similar usage at the same age began to see his effectiveness begin to decline sharply and began to break down physically. I wouldn't be surprised in LeBron experiences the same thing. Is a Lakers team with Davis, Kuzma and a declining LeBron a title favorite? If LeBron somehow pulls together a healthy season where he's still 80% of his former self and they can add some low-cost vets below market value because they want to chase a ring...maybe. But, anything after year 17 would be breaking new ground, and he already spent last season dealing with injuries.