Just as many fellows have mentioned and explained, I guess one thing that is already great is the training system. It needs foreplanning, different strategies, adjustability, etc. and everything is pretty good with the system.
Every time I play NBA 2K, I spend hours at MyGM mode. One thing I would really love BB to have is a simple minute-management system. We already know the defaults through the walkover matches: 36-10-2. The starter takes the big chunk, then the first sub and the reserve player.
If we could manage the minutes just as real-life coaches do, that would enhance several things in the game:
1) Tactical depth
Now, we have offensive tactics that most people are grouped around only a couple of them, defensive tactics that there are basically 2 schools of thoughts (M2M and 3-2 zone), and GDP that most users don't even try using against human teams unless they have to gamble to win.
Through the complexity of design, the minute-management system can increase that. Indeed, there should be some defaults (or let the coach decide) for those who don't want to spend time on that but knowing that you could save your team's energy to the last quarter definitely elevates your team's chances against better-equipped teams.
2) Training
As it was unveiled in the last season's Q&A and Season 53 news, short rosters are getting penalized now. There is another thing that gets penalized: Training youngsters.
As of right now, we don't know how effective the stamina drop/skill drop will be but if a player's skill decreases to the point that he no longer is useful in the game defensively or offensively, training youngsters is going to be non-viable for the most users. If most users give up on training for the sake of being successful, the player supply will go down and that would result in an imbalanced transfer market where the richest teams will be able to acquire the majority of players.
If playing for the whole game increases foul proneness, that will also decrease the player supply in the transfer market.
However, if we could manage the minutes (even the simplest system), that would solve the problems in regards to training. For the one-position training, we just have 144 minutes to allocate in a week and that would be easy to solve.
3) Economy
This is obviously a result of the training section but it would help the overall economy. This is my third stint on BB (and the longest) and as an economist in real-life, I noticed something that you would not see in real life: an 18-year-old 60 TSP guy with an MVP or higher potential is sold higher than a 24-year-old 120 TSP guy. In regular economies, you get the raw material, you process it and you sell it for a higher price. Why? Because processing takes time and money.
However, in BB, the raw material is more expensive than the final product. Why does it happen? Because people know that they can't find a better guy; thus, they reserve the best fruit for themselves. You usually have 3 slots to train. 1 is the best starter, 2nd is the sub and the third one is there if everything goes alright. I started training the big guys last season and my third slot got merely 5 weeks of full training. Under such conditions, would I sell my first or second slot? No way.
That's where the minute-management system would step up to save the economy. Your third option would be to make money even if you decided to keep the number 1 and 2 options for yourself.
It became more like a suggestion rather than an appreciation message but finally knowing that some BB may actually read it tempted me.
Plus, whoever/whatever was in charge of the off-season process, keep him/it, please.