Hello, I have been using these keyboard shortcuts for sketch constraints and they are super fast to learn and use! Thought I would share, and I hope that you may find it useful. And perhaps, there can be some included default hotkeys for constraints in Fusion 360.
These hotkeys are arranged so that the left hand can complete all shortcuts without lifting pinky off of the shift button- which makes them all very fast. Logic behind each designation found below:
Horizontal/Vertical = Shift+h
Coincident = Shift+v (icon looks like a v)
Tangent = Shift+t
Equal = Shift+e
Parallel = Shift+a
Perpendicular = Shift+r
Fix/Unfix = Shift+f
Midpoint = Shift+d
Concentric = Shift+c
Collinear = Shift+y (icon looks like a y)
Symmetry = Shift+x ('x' is symmetrical)
Curvature = Shift+b (capital 'B' contains matched curvature)