I am not thrilled with introducing extra clicks in the business end of modelling by default. It also depends how accessible and prominent(the task pane becomes) Are the commands combined there as well?
In general I think it is extremely important to keep the often used tools in any area where a creative process is happening as accessible and clear as possible.
Pad and pocket is also the first place new users will cut their teth, it does take a bit more imagination to grasp the combined icons meaning.
Will the old style icons and commands be available for adding to a custom toolbar?
How will the python functions for these functions be, will they also be combined? or will you still have separate commands for Pad Pocket. ?
Of-corse as a KDE person I would prefer to have this configured as a preference, but split icons by default.
I have not tried the Part design Next branch in ages. Will build and test again soon.
My 3 cents
Thanks for the great work you do, and for the possibility to share my thoughts