you could use the somewhat-emacs-like "shortcut": Ctl-A-Ctl-X-Ctl-Z :-)
if prefer less keystrokes (and/or don't want to reset the entire canvas) this should be easily doable with a gui-plugin.

afaict, this is the only feasible solution to provide a generic "reset to default parameters".
to implement this functionality without a "hard reset" would involve highly objectclass specific code.

one possible solution would be to create a special "reset" 'message' (of type A_GIMME), that would allow the object to implement a proper reset without re-instantiation. if the object does not provide one, it would default to a free/new cycle.