Variations of your proposal have been proposed all those years. They are all mostly nice but they would also mean a completely different game and thus are hard to consider.
However, there is an implementation that could be made and which would allow more variations, would allow some secrecy and also would keep the spirit of how BB training works:
- training should be possible not only for the player's designated offensive position but also for the player's designated defense position.
For example, you have a perimeter player that you want to develop his inside skills, than:
Player A - offense PG defense C
Player B - offense SG defense PG
Player C - offense SF defense SG
Player D - offense PF defense SF
Player E - offense C defense PF
You choose that you want the players who defend as centers to train ID, so in this case player A receive training.
In order to keep things more realistic, this could be the default way to train defenses.