I think that the issue of text editing and typesetting should be held separate. When editing a text, I am operating on a character string. In my editor, I can

I think that the issue of text editing and typesetting should be held separate. When editing a text, I am operating on a character string. In my editor, I can jump forward and backwards over sentences. The editor can discern these periods from others because they are followed by two space characters. When typesetting a text, it gets a proportional font, and the space left empty between sentences is set as the typesetter wants resp. the typesetting rules dictate. Do not confuse "two space characters" of a character stream with "a double space" of typeset text. Of course, WYSIWYG ("what you see is what you get") editing of text would need to be very much aware of such issues, but mostly is not. I think that WYSIWYG editing is a bad idea, anyway.