I'd love to see an ability to play more positions. I hate being limited to CF and LF, C and 3b, or SS and 2B. I want to be able to super utility if I so choose.
Season individual goals for xp. In madden you can set a goal for 4k yards passing, 30 td,s etc. Let em set goals for myself in RTTS (30 hr, 40 sb, 150k, etc)
Badges and upgrades. I love the 2k Badge system, and I wish the show could do something similar (I know DD has something like this now, but I hope RTTS does too and allow them to be upgradable through hard work)
Allow me to pitch free agents. Players like hearing from other players. If I can help recruit a superstar to my team (similar to Trout's impact on the Angels signing Rendon) then I want to be able to help build a winning franchise.
Just like real life, let me take a prospect under my wing in spring training to help groom. Happens all the time as AA and AAA prospects train in the off-season. They gravitate to the veterans to develop more and learn.
Allow for off-season training and progress. it's 2020.. Players don't just stop working out in October and start again in March. A lot of young players work year round on strength, conditioning, etc to get better in the off-season.
Separate the DD and RTTS equipment. Let me buy RTTS equipment with my contract dollars. Keep the DD equipment cards in DD or if I have a DD card let me use it for both, but if I play RTTS, I should have access to top end equipment if I'm an all-star making 25+ M a year. I shouldn't need Virtual stubs to buy cleats, a bat, gloves, etc.
XP gains change vs difficulty played... Or make initial stats more realistic based on how I did at combine, etc.
Free interaction between games. 2k's open world pick up area is neat. Allow me to train in the gym, cages, gamble stubs on daily games, buy gear from shops, etc.
LET ME TALK TO MY AGENT WHEN I WANT... I hate having to wait 4 months when I'm unhappy with something or if I want to make a change.
(These are just for RTTS, but I ahve an even longer list for franchise)
I've said to separate RTTS and DD gear. That way the player can use the contract dollars to buy Gear, Livable quarters, a trainer, pay your agent, etc..
I personally don't care about tattoo's, but I'd like to see some other cool cosmetics, like clothes, weights for a training room, etc... Maybe watch film on pitchers you'll face to get an edge. (or batters if you're a pitcher). As a RPG.. It would be really cool to see SDS allow the user to make it what they want.
Taveras for Texas is pretty nice at CF. He's a solid player with 70-80 grade speed. His fielding is Gold too if I'm not mistaken.