ooh lots of complicated mel talk
babyduck: you know you said you could make it so when you click a button in the mel box and it keys (turns it orange in the channel box) and when you click again it deletes the key? mayb when you scrub the time slider, and it reaches a point where the object's attribute already has a keyframe, then in the mel window, that attribute would be yellow as well, just so the user knows if there already is a keyframe, cos otherwise you could go around deleting all the keyframes you have when all you want to do is SET them
or
what about in the script box, you have 2 buttons for each attribute in the channel box? one for key, one for delete key? but i spose it wud still have to turnorange for you to no if there already is a key or not

*EDIT*: just had a thought, would it be easier, animation wise, to have a slider in the mel script box as well? cos then you could do all animation in the new window and key it really fast as well without having to go into ur viewport or channel box
there shud also be a button at the bottom which says "Key All" hmm, wonder what that would do