Things I'd like to see in-game
Additions:
I did find it weird how at one point I released a single coming off of a 100% fan satisfaction one, got 8% fan satisfaction, but suffered no consequences for it as the sales between the two singles increased, leading to my next few ideas:
Subgenres and music trends
I saw in an early demo from 2016 that there was an idea to have the current in-game major genres like Pop, EDM, Rock, R&B etc. behave more like skill trees which progress through subgenres/genre families rather than solely increasing in efficacy through the research points. Like EDM would be an umbrella for Tropical House, House, IDM, etc. and these individual subgenres could be either trendy during the time of release or rising trends. I thought this was a great idea and was sad to not see it in Beta. The people I discuss this game with share this opinion, some noted there's no real incentive/push factor to change up what type of single you produce unless you're a completionist who wants to do all the genres. Some genres will ALWAYS be unattractive to casuals, core, etc. Doing the same love>cute>pop progression will ALWAYS sell well with hardcores, even on the 20th iteration of that combination. So why think about the singles production anymore after you hit a certain threshold of fame?
With the trend+subgenre system, I could see more engaging game play, and gameplay that evolves your tactics: making your single a subgenre that's a rising trend could boost its sales and appeal among casuals+teens/YAs, and usher the subgenre into being a current trend. Current trends could increase that boost even more but over-saturate that sound and push it into being a "past" trend which might cause fatigue and penalty/decreased appeal and sales and encourage players to explore other subgenres and try to either chase or predict the next trend.
Fan feedback/SNS feed
I also saw this in the demo and thought it was a great idea: Fans giving indications of what styles might be upcoming, if they're getting bored with the group's current image, which idols are on the rise/descent, current events etc. Imagine if there's a political election coming up in-game, so releasing a political single might have more efficacy than usual, or the hardcore base is under a lot of stress as of late so an anxiety single has more potential.
Subgroups/Sister groups
Thought of this because it's difficult to A) look at the girls when they're all on one menu, especially as you add more B) it's hard to organize the girls and evaluate who should be in what single C) I want to use all my girls and produce different types of singles but with frequent release penalties it's difficult to build them up.
I think adding in a system like how AKB has SKE, NMB, HKT etc. or 46 has Nogi, Keya, Hina etc. would be very useful: Players could have all idols under one group, but sort them in established subgroups/sister groups for convenience AND in-game bonuses. For example, I could make a subgroup where I put my girls with high Sexy stats, and another for girls with high Pretty stats, and have the first group release singles targeting men while the second targets women. An in-game bonus could be that these groups still need a month between their OWN singles to avoid a fatigue penalty, but releasing within this period of another sister group's release wouldn't trigger it. To balance this out, maybe hardcore fans would be less willing to buy each subgroups' singles/only their favorite subgroup, but would combine for the full group singles depending on team composition.
Additionally, maybe girls could form cliques/relationships based around their sister group as well? Fans/casuals could associate certain lyrical styles, dances, and genres with certain sister groups and find it off-putting if a sister group suddenly changes its style. The fullgroup could have combined appeal metrics/demos but negative/positive opinion of subgroup could possibly not have a direct influence on another sister group, enabling experimentation. And if there had to be a distinction between what constitutes a full group single vs a sister group single, it could be that any single composed of girls from more than one group/girls who are groupless become fullgroup by de facto.
Rival Groups
I think I've read something about this being implemented? I think it would be a great addition. Possibly siphoning fans and contracts/casuals away, forcing your group to change up their image to compete: I'm really looking forward to that if it's happening. I also thinking groups already existing when you show up could help spice up the early game and require you to employ different tactics in each playthrough if some semi-randomized groups of various levels of establishment were there to beat and/or also on the rise all the time. (For example casual attention is already on a randomized "sexy group who does energetic pop songs" so you either have to beat them at their own game or specialize and outdo them at something else if you want casuals/contracts).
Changes/Suggestions:
Producer role/points
I've seen a few people bring up how the Producer is a major bottleneck right now: Every project and socialization has to go through them meaning they can't accumulate research points for media and lyrics at the rate every other role does. Similar problem with how the Manager can't accumulate points if you're searching for business deals and pretty much requires two, but you obviously can't hire a second Producer. I think either making a new role that works on Lyrics OR allowing the Producer to gain Research points even if they're working.
Estimated sales/concert changes
With concert prices, I wish there was a button to just immediately set price for maximum profit OR maximum attendance, since I imagine these are the only two prices relevant to a player, rather than having to fiddle around with it. I also feel like concerts might be a bit too OP in how quickly they start doubling their production costs if you just up the ticket price. I was able to score 20-30M on my second/third concert despite having 33% attendance. I think having a negative effects for trying to abuse concert pricing/going to too big a venue could be good, like having an expensive price or a concert with only a 1/3 of the seats filled could give groups a hit in buzz and bad press?
Additionally the songlist available for organizing the set starts getting overwhelming very quickly, a different menu style might help. I also think there's really no incentive to use your oldest songs at the moment, when in real life several old songs continue to live on in setlists. Maybe there could be bonuses for including older songs such as "fan favorite" for the debut single, the first single to sell 100K, the first single/center appearance of a popular member, etc., to give the old songs some use.
Relationships/events/conflict
Not sure if it's just my playthroughs (Because I do not use the dating options at all) but in all of them I only get some fight events with not very noticeable effects other than sometimes a slight ding to the relationships. I think some insertion of qualities like jealousy/rivalry between current top idols, between rising/pushed idols, and between old guard and new guard could add some interesting dynamics. (I noticed how in the demo it wasn't just moving a girl to a farther back position that makes her disappointed, but ALSO bringing up/adding a newer girl or a girl who was behind her can sour her mood, which I didn't notice in the Beta.)
I think it's great how public spats/resentment can put your contracts at risk, that bad chemistry and bullying can take idols out of commission and lower the efficacy of singles. I'd like to see more of that kind of thing, both in ways you've currently implemented and in new ways.
Elections/Senbatsu
Lastly, I think the elections are my favorite part of the game, concurrently organizing a single and concert and seeing how the girls' ranks change is challenging and a lot of fun. I think what would be a great addition is emulating what AKB does, where the senbatsu election members lead a special single after the election. Maybe in-game you could do something like the Top 10 instantly (Or on a 2-week timer) releasing a fatigue-free/frequency penalty bonus-free single with increased hardcore appeal or a stamina-free marketing plan/a special marketing plan reserved only for the post-election single? Or some kind of special benefit only reserved for the post-Election single.