RTF text spaces are two-edged sword. Easy to disparage is the ability to import (unexpectedly) badly formatted styled text. However, RTF also - used with care, allows a useful dredge of styling that aids comprehension.
Thus I wonder if the option here is to:
a) allow only plain-paste only, regardless of source style. IOW, the user my, by choice, add styling. But, for notes so marked, they will never import styling via paste or drop.
b) have plain text-only notes.
I can see some wanting both/either. For my 2¢ as a TBX user , (a) seems a better and more flexible option.
In context, a glaring hole in current controls is you can’t reset the selection(or whole) note to defaults. Margins/tabs have to be done separately from text styling. Even if the latter is needed, it shouldn’t require two discrete menu commands to scrub bad formatting from $Text. Ideally, the task should be one menu option and an action to require cleaning at scale.