Various things I found around, which probably don't matter and will never see the light of day, and it's also a lot of interpretation and guessing and not confirmed in any way, but it's funny to think about these.

• “Hit [x] WONDERFULs” ACs have been implemented since the start. ¹⁾
  • While you might think they'd never be used because Autoplay would make them literally impossible, Autoplay is actually not locked to Greats. The game specifies what timing the Autoplay should hit every single note with. So if this type of ACs ever appears, Autoplay might just hit exactly enough WONDERFULs to clear the ACs, since a certain amount of notes have their Autoplay timing set to that. ²⁾
• More unused ACs: Heal a certain amount, gain a certain amount of Shield, get a certain amount of Voltage where only a certain Unit type counts³⁾
• There are some values hinting at possible Live Multipliers (x2, x5 and x10). That was probably dropped in favour of Skip Tickets. ⁴⁾
• The song played in the Super Stage in Chapter 2 depends on the Story before it - the player chooses who will win the competition. While it is not possible to see in-game (because the Super Stage is hidden until a choice is made), if the player was somehow able to skip the choice, the winner would be… Kasumin! ⁵⁾
• The reason why you get 100 event points after every SBLSBL: Short for "SIFAS Big Live". A monthly co-op event where 20 players go for Group Goals and fight for MVP Titles.➔ Learn More live is that it was planned to make this value dependent on your individual Voltage rank (as in S/A/B/C/D, not the placement). It seems that this was dropped at some point, so now the database just sets the reward for every rank on every SBL song to a fixed 100. ⁶⁾
• It is possible for the game to show a video file instead of the 2D/3D MV in the background of a Live. This has not been used yet, though. ⁷⁾ Debuted with Niji-iro Passions! for Niji Anime Ep2.
• The permanent Adv+ difficulties are not permanent - they will expire on the 18th July, 2025 at 15 JST. ⁸⁾
• Due to some oddity with how lives work, apparently every stage has to have the trophy missions defined, including those you don't play the regular way. As such, the Queendom MV stage in Chapter 20 would have the regular 2/3/5 star split if you S ranked it by reaching only 4 voltage… if there was any way to actually play that song.⁹⁾