But he is never going to get in great shape. You can tell by his body type. He has a wide frame that is going to continue to hold onto baby fat as he gets older... and the baby fat turns into adult fat. The fact that he has been pretty successful in his young career also likely means he won't be motivated to take any extraordinary measures to improve his conditioning either.
In all likelihood, he is at his ceiling right now... which is fine, as he is quite successful at what he does. But the really generational guys like Jordan and Lebron, when they were four years into their careers, you knew they were going to get better because they would continue to become more athletic as they matured. Doncic isn't that guy. In fact, he is probably going to crest relatively soon and likely have more issues with injuries and conditioning as he hits his latter 20s.
Of course, there is always the possibility that he gets teamed up with another star teammate or two sometime later in his career. But again, I don't see him as a great complementary player the way Magic or Bird were. Frankly, I see a lot more of Harden and Westbrook - a guy who will put up fancy stats and make lots of fancy plays, but isn't going to be the transcendent player that some people keep trying to make him out to be.