1. My bad, didn’t know about add clone shortcut so that’s solved for single frames! Is there a key for reducing clones too?
Drawback is that it doesn’t work for multiple frames so when timing a larger set of drawings it might be useful to have a context specific right click menu for setting selected frames across layers to twos or threes or fours (longer holds are anyways done by dragging). Or alternatively ‘ could work for selections too (and extend/reduce selection as needed, so that the shortcut could be hit repeatedly – this might fit AP approach and would be better in general).
2. My preference comes from Toonz and others like it where the concepts of level (stack of cels) and xsheet (how to shoot these cels) are separate and the drawings are numbered (so camera operator can skip frames). As a concept it might not fit AP so I thought of something “simpler” like a bin where the unused cells would go for safekeeping. As you said, it probably wouldn’t work either and be messy/unclear anyway.
Your workaround is good I think, but maybe it could be enhanced with a feature to duplicate/clone a whole level (in addition to moving layers around). In this case one could (if wanted) emulate paper workflow by doing all the drawings first on one layer (or more), duplicate it with clones (hiding the original) and work on the cloned layer by timing, deleting and copypasting frames as needed. Might be nice and simple (as all the drawings can be found in xsheet, nothing is lost by accident and the whole workflow would be optional)?
On a sidenote what are the plans with xsheet, will pegs be animatable (moved manually or with curves and the like) or do you see walk cycles across the screen and the like being done in compositing?