If you guys are interested, I've got some ideas that I don't think I'll use:
- A game where you can do rewind to some seconds in the past to gain informations or items without anyone knowing (like killing a guard to get the keys, then going back and still have the keys without anyone noticing). You can also do things like opening a door that has a set time of being open, then get there and even if it's closed go back to when it was open
- A game where you do something, then restart, but the past version of you is doing exactly what you did before. Not very original, it's common in puzzle games, like Talos Principle. You can do things like standing on a button to open a door, so your future you will be able to go through the door (basic example)