I see what you're saying - that by changing the FPS to 12, it effectively can set it to 12 hashmarks per second on the timeline. So if you wanted to do what I was suggesting, you would set the FPS to 12 before animating. However, this is both unintuitive, and duplicates the function of the "speed" slider in the same menu, because you have 2 methods to modify playback speed, but neither of them modifies the timeline hashmarks or keys.
Question - when exporting to AVI or MOV, does the "Dopesheet FPS" setting remain in effect in the export? Or does it export at 30 FPS regardless of this setting?
What I was actually suggesting is that the FPS slider (or rather, a slider in the settings menu) would change the timeline's number of hashmarks per second, without 1) changing playback speed, or 2) modifying the position of keyframes relative to seconds. So the animation would play at the same speed, but simply changes the hashmark interval. This would allow you to animate at 12 "hashmarks per second" (allowing you to be more efficient at animation), and then change back to 30 for polishing the animation. But this only works if the hashmark interval changes WITHOUT changing the speed... which you currently cannot do with the FPS slider as indicated. I suppose you could set it to 12 FPS, animate, and then set it to 30 and stretch your keys out to 30, but that would be a lot of repeated adjustment.
I'm assuming that the hashmarks themselves must be arbitrary, since the editor has an effectively unlimited FPS, and keys can be set to arbitrary positions between hashmarks... so why would the frame hashmarks themselves be the one thing that can't be edited? You can freely edit speed and keys, but not the frame interval?
I also wish that the "Editor Frame Rate" option in settings could go below 30 FPS, and that this was in the Playback panel rather than settings. Currently the only way to view the animation at true 12 or 24 FPS would be to key every frame and set it to Stepped interpolation. It seems like this would be easy to implement?
Also, is there a way to easily view all keyed bones in the dopesheet? I've tried using the lock, but if I ever deselect the lock, it's almost impossible to find all of the keyed bones again in a complex skeleton.