First, feedback about existing functionality:
One use I found for them that I like and works without much issue is creating different takes for camera or character moves, and being able to really quickly switch between them by changing the slot on the NLA strip. Outside of that, merging or actions or adding slots is pretty inconvenient when also working with the NLA editor. In my testing I would have to assign the strips action to the scene objects to make changes then unassign again, which was inconvenient.
The ‘Only Show Slot for Active Object’ filter should instead be a ‘Only Show Slots for Selected’, and work the same as ‘Only Show Selected’ works.
Locking and hiding slots would be very nice to be able to see other slots keyframes without accidentally editing them. In addition to the previous suggestion, I think these would make working with them more comfortable and less error prone.
Ideally there’d be an option to duplicate a slot with its keyframes. As is, copy and pasting keyframes currently pastes to a seemingly random slot. It should paste to the active slot, or at least the active object’s slot. I had a lot of trouble just trying to copy keyframes from one slot to another, even in the same action. I think the only way I got it to work was separating the slots first, then merging after copy pasting.
Couple bugs:
Trying to delete an unused slot crashed blender, and after a couple crashes this way, blender would crash on startup and I’d have to restart my machine.
Searching fcurves didn’t update the UI and clicking channel groups to expand would cause them to disappear if they didn’t contain a searched fcurve.
What I hope they’ll do someday:
I’d really like some way to use slotted actions like scene strips in the sequencer, but in one scene. Being able to group all the animation for a shot into one action seems like a great use case for me, if they could be manipulated like strips in the sequencer. They could be a way more usable and faster than scene strips.
Also/Or: Better use with the NLA editor. Such as merging actions from strip selections, and maybe linking strips that share an action like audio clips in the sequencer. Might not be as practical as being able to manipulate slotted actions as strips on a scene timeline.
I think maybe the use cases I think of and have been trying to use the slotted actions for need the actions (or their strips) to refer to the datablocks they animate in the scene and not the other way around, but I don’t know if that dramatic of a change is worth considering.
Thanks for your work 