I'm a big fan of Football Manager, I started playing at FM2014 and have owned all PC and Mobile versions since. I'm just gonna be giving my suggestions for PC only.
1) An improved engine - I feel that a new or improved version of the current engine is needed for better graphic fidelity and smoother / more natural looking animations. Don't get me wrong, animations were an improvement here, but graphics weren't so much of an improvement.
2) More types of tweets - I tend to see a lot of the same tweets, word for word, on the social media feed. I think there needs to be A LOT more variation just so it doesn't get old so quick.
3) More social media - I think the inclusion of the twitter style feed was super cool and would like to see another one maybe in similar fashion to instagram. Here is an example for how his could work: Manchester United sign a player like Kasper Dolberg. Too announce the signing a picture is posted of him holding or wearing the Man United kit and there's a little caption and hashtag or two. Then the player would also post something like this, as well as the league, and maybe fans too.
4) More User Friendly UI - I don't have many problems with the current way it is but I would like to see a redesigned UI that just flows better and is simpler to use. The current UI can be difficult to figure out for new players even with the hint system.
5) Licensing - I know it is expensive, but I need more than Everton and Watford licensed when I drop 60 USD on the game.
6) Better training system - Maybe something kinda like Fifa introduced in Fifa 16 except instead of 5 players, you can do the whole team. An example: You can watch the training, it would take 2-5 minutes. All players do the training they are set to do as well as a generalized team training. After it is done, you can view a training report and see which players had a good session, bad session, got hurt, improved, or worsened, etc. If you don't want to watch the training, a simulate button or automatic button or something should be there.
7) Better youth system - Growing youth players can be super super difficult. I'm not sure exactly what needs to be done to improve this but I do feel it could use a change.
This is all I could think of for now. If you've got any ideas, post them.