As already requested on Discord, i'd suggest a Connected Plane - chisel mode.
How exactly it works:
-The main method is just the "Plane mode".
But it also applied to everything that is connected to the clicked part using PLANE mode.

When you keep chopping away the upper part, at the end this will be left:

Basically:
Plane chisel mode. But everything that is NOT directly connected will not be chopped away.
The best way to test this i using the pre-rebuild c&b, this has this exact feature.

Same suggestion. (Actually this is originally suggested by me)
I hope If any part of a block which is not connected to any other part of same material can be removed using a particular chisel mode. This will bring convenience to the process of any chiseling.