I remember a few NBA Live's ago your free agents could refuse to resign, that'd be interesting if re-implemented slightly differently:
Players contract ends at the end of the season/playoffs, you get a message on PDA saying the player wishes to test the FA market and will not resign with the team, then kinda like with trades on your PDA you can choose how to respond to the news.... One response should be "sign and trade" which will make the CPU look for good trades based on team interest, so you dont always get a 85 rated player for your 85 rated player, you might only get a 70 rated player that fills a big void on your team because your 85 guy fills a big void on the other team (like the vince carter trade) .... something with sign and trade would be great coz i liked the idea that my players could refuse to resign with my team, but i hated not being able to get -some- value out of it.
Rookie Draft:
I think the day before the draft there should be a chance to trade draft picks and a few CPU teams should shop their picks, offer a trade or two, just to make things more interesting....
3 Team Trades:
They happen in the NBA, so they should be in the game, its EA's slogan for christs sake!
Free Agents:
Be able to resign your FA's that have tested the FA market after the FA signing period even if your over the cap, the CPU does it! ...I think it should be restricted though because you could drop your top players, sign other teams stars, then resign your stars that dont get to sign elsewhere which would be unfair.
Prolly more things id like to see, but thatll do for now.