Hello,
Maybe this propo is already in Jcome minds somewhere but did’nt found something similar.
What do you think about transform tool panel host keyframe edit dialog when selected (has in this quick composition) :
For sure this screenshot is not a definitive proposition !
Valid button is not needed, a cancel button can be add, text but icons, someother of waypoint right click entries can be also included …
(i have put some screewdriver and solder things in my synfig dev laptop… i cross the finger before remount it 
see(:ya!