I too believe there is plenty of work that can still find it's way into the game. In my opinion, a lot of that is behind the scenes stuff though, which doesn't carry the same weight as "new features!"
I think the AI can always be improved until just this side of human.
Negotiating contracts and extensions and being well aware of how humans can still out think them when adding opt-outs, options and buyouts, can always be improved. I think you can always aspire to better game management, lineups, rotations, player rest, small ball tactics and much more.
That said, I can always see the need to never be as "smart" as a human because that too is subjective and the game could get far too hard for the casual and new player. And I'm sure a first-timer doesn't want to immediately match wits with a ML manager/general manager AI.
But it would be the ultimate test!