I've put these in the order that I'd like them. I apologise for any grammar/spelling mistakes, I'm up late looking after my unwell mother and nephew.
1) Ladies players, staff, teams and leagues. I'd love to be able to manage those leagues, and I personally have no objection to ladies being on the staff at a club, being managers or playing the game.
2) Increase the communication you can have with your chairman. For example at the start of the season you get told your cup goals, which is fine. But if I get drawn against a bigger team early on, I'd like to be able to go to my chairman and ask for a bit more understanding with the cup goals.
3) When talking to players who want to be picked more often, it still feels like you don't have enough chance to say "You haven't been picked because you're playing badly" or "Well stop getting sent off". It also feels like too many players react badly to it. I will say that I am pleased that this has improved greatly from the days when a player would demand to be picked when they were out injured with a stress fracture. Seriously, for those who don't remember, it used to happen and there was naff all you could do about it.
4) Staff: I'm not a big fan of coaches & physiotherapists being grouped together in "other staff", I'd much rather they were kept separate. I'd also like to be able to bring in psychologists and analysts. Obviously these roles would likely only be available to higher profile clubs. However with this, I'd like to be able to negotiate with the board about what staff I have, i.e. "You're allowing me 5 coaches and 3 physios, please may I have an extra coach and in exchange for a physio?". Also with placing an add for coaches, I'd like to be able to specify an "attack coach" or something like that, and also being able to ask for a certain amount of international caps, goals/clean sheets etc.
5) Being able to offer things like houses, bringing family over, jobs for family for overseas players, especially for the younger ones. By the way SI, this has been asked for a lot in the past.
6) If you have a transfer arranged, I'd like to be able to be able to use the transfer fee and have the wages available so I can work on a replacement for that. It's really irritating that you know you're going to have the money and wages available for the transfer, the player is available but there's nothing you can do about it, and I think that would be a really good addition to the game.
7) I know that there is a potential legal issue here, but if possible I'd like to be able to change kits every now and again, even if it was done with an in-game kit generator. Fan & player reactions to kits would be welcome of course. Again, something that is repeatedly asked for.
8) Players being affected for incidents off the pitch e.g. controversial social media updates, car accidents, things like that.
9) Increasing what you can do with managers and agents you have a good relationship with so that you can negotiate "behind the scenes" to get players at a better price, both on loan and with transfers. In addition to that I think it would be good if you have an injury crisis, a manager you have a good relationship with could contact you and offer a player on loan at a better price. Obviously being able to reciprocate would be good too. It would have to be implemented properly however; I don't want to be falling out with another manager asking for a player on loan, I reply "sorry, I don't have someone in that position" and them going overboard. That would be silly. An addition to that that I'd like would to be able to get advice from higher profile managers and/or club legend, especially when you have a match against a much higher level club, have a difficult run of matches or are in a bad run.
10) If you do great things at a club, I'd like the club to be able to pay tribute to you buy naming a part of the stadium after you or placing a statue of you at the ground. I'd also like to be able to organise tribute matches to legendary players.
11) I'd like some historical challenges as well as what there are at the moment e.g. being able to manage a team in the first season of the Premier League, tournament specific challenges (2014 World Cup), managing a team in the first season of the football league etc.
12) If you ask your assistant to manager your team in friendlies, you can only ask them to play with your tactics. I think it would be a good addition if it was possible to ask your assistant to come up with their own tactics. This would be especially good if managing a club you're not familiar with, so you can observe the assistants ideas and things like that.
13) I like the current career mode, but I also quite like the idea of a "full career" when you start out as a young coach of an under 19 team or academy and work your way up like that.
14) I'd like the languages you can speak to be able to have more of an effect on the staff and players you can recruit. For me it just doesn't seem to have an impact on that.
15) A small revamp in the training menu so you can actually drill players, not just on new set pieces but also if you decide to change from regularly using a high defensive line to a deeper defensive line, or using the offside trap. Also instead of being told you have a pre-season training camp by the board, I would prefer it if I had the choice.
16) Instead of being able to upload a photo of yourself when starting a game, how about a face-generator working with your webcam. It creates a likeness of your face and then your face ages as the game goes on, instead of being unaffected by a long career.
17) Being able to investigate your physio team if you have an injury crisis. Or is that a bit much?
18) Scrap the tax payments and things like that. Let me make this totally clear; it's a very in depth game, but it's only a football game. I have enough of taxes in the real world without having to deal with taxes within a game. I hate that feature and it needs to go away.