ACE-DL has a rewind feature, but it is not as good as it could be: [https://youtu.be/wIKGvpnJLUo Demonstration of rewind in ACE-DL]
At the moment, only Only the RetroArch CPC emulator has a proper rewind feature: [https://youtu.be/YwilYlSe5LQ Demonstration of rewind in RetroArch]. To reverse the game, the user press and hold the rewind button. And at any point, releasing the button makes time goes forward again.
A very simple approach would be to make a SNA for each frame and limit the RAM snapshot to 128KB, which is ok for 99% of CPC software. For a 10-seconds long rewind functionality, only 64MB RAM is needed (128KB * 50 frames * 10 seconds).