I'm not a fan of the concept of event boosters. Every event, most players are only interested in one or two girls. Allowing them to obtain them for free removes any incentive to spend real money on the game. What you're currently suggesting would allow players to obtain two event girls for each event. The event idol isn't the popular girl anyways and it's usually the troll drops/Epic Pachinko drops that players would want in the first place.On top of that, your suggestion would essentially allow anyone to obtain past girls if they wait long enough without having to spend a significant amount of money. This would reduce Epic Pachinko drops to costing 600 kobans instead of 900 kobans AND allow users to select who they want, which is ludicrous.

The current system rewards players for spending kobans and obtaining past girls in the first place and your suggestion would essentially punish older players for having spent money, while rewarding free players and essentially encouraging all players not to spend money/spend very little money on the game.

The team would basically have very little overall income if players were to obtain the 2 girls they cared about for the event in the first place for free. The game would not be self-sustainable and continue to take a loss. Please keep in mind that the game developers are working on the game full-time.

My personal preference would be to bring back each event's specific girls in the form that the original appeared while introducing a new wave girls. This would give older players something to go for while giving new players access to the event's past girls+ new girls. There would be two event every year, once during the anniversary and once during the New Year, where players would be able to obtain past event girls through a special Pachinko for kobans at the standard costs.

This would continue to keep the game self-sustainable while keeping everyone happy.