It makes sense to enable this mode when editing objects with building=*, but not natural=water (and such).

https://josm.openstreetmap.de/wiki/Help/Action/Extrude
Not everything must be implemented: "ctrl" mode (as default way to move way segments) and probably "basic mode"

It makes no sense to draw arbitrary shaped object, then use Q tool, then correct some portion of the object, then press Q again.

It is time-consuming to human to draw 90-degree objects using pattern mentioned above.