I don't think drastic changes are needed to many things. I think a drastic change is needed for one thing -- injury recovery.
Some other things that are less important, but ive heard multiple people say they want are below, but injury recovery needs to be #1 priority.
1. Injury Rrecovery
The Rest:
a. Extreme stadiums. Even if the stadiums are fictional or based on historical stadiums like the Polo Grounds, it'd be cool to have more choices of extreme hitter and extreme pitcher parks. Many people find it fun to build a team around park factors and as much as the latest stadium update made the stadiums more like their real life counterparts, it certainly diluted the experience because now most of the stadiums are close to neutral.
b. Ability for commissioner to choose if an NL league has the DH or has pitchers hit.
c. create a player: this is two fold -- i. a fun and optional thing to add to pre-season activities; ii. second round picks that make it past arb1 in the mlb are a rarity in hbd, this could help fix that. Obviously hbd owners would manipulate it so it would have to have a cap on the number of players each owner could create (i.e. 3), a cap on the overall rating of each player created (i.e. under 65 overall, under 60 overall under 55 overall) and a cap on max ratings (i.e. 85). This can be further discussed.
d. adding a withdraw and return to the coach contract negotiations screen to avoid the extra clicks.
e. increase supply of fielding instructors by 25 to 40 percent.
f. Adding true AI teams and giving commissioners the ability to start a season with up to X amount of AI teams
g. 26 man mlb roster