i really like your suggestions, especially since the game does get stale if you play it long enough.
I think the issue is the core gameplay loop, which boils song to single --> single --> single --> single, with the odd concert here and there, which is made worse with sister groups (across all my groups, I was pumping like a single a week). This can make gameplay feel stale after a while so I'd hope the dev can think of something to mix the gameplay loop with other elements.
If there's any one feature to prevent staleness that I really wish the devs add, it's graduation concerts. I think it shouldn't be too difficult and would spice up mid to late game a lot, when your key idols are graduating, Plus you'll get a great, memorable and custom send-off for each of the important girls.