hi,
first of all i would thank you all of blender team and all of blender community for all efforts
my suggestion to make
1- undo & redo for viewport user presp/user ortho scene (as camera undo & redo[move/rotate] )
2-add units for get 3d blocks from other 3d program when ,choose this new unit like other 3d program unit get imported clean scale object have the real scale without rescale it