Some suggestions I have:
- Other people have mentioned this but facilities/trainers are realllly expensive and you need them for singles so you pretty much have to cheat in the beginning, and I think for a new idol group singles would be the most important thing?
- A cool mechanic down the road would possibly be music videos, maybe with a little minigame like concerts? Possibly picking the theme of the video to match the song or something like that.
- Debuts for new idols/subgroups would be nice
- More fan interaction, like fan clubs, stans for each of your popular idols, having them try to raise views on music videos/getting more people to buy singles...
- I tentatively want a bit of a boost in how much a stat increases based on the level of the trainer, possibly also scaled to how high the stat is on the idol. This could easily be really unbalanced though which is why I'm tentative, maybe down the road when you have more stuff for idols to do/train in it could work. However I think it would tie into how if you took some girl from a backwater town and gave her world class dance and vocal training she would improve pretty quickly.