\ is not only an escape character as you define it. Sometimes it means the exact opposite of that: the following character has special meaning, e.g., \n \t etc.
And it is also not the case that \ only applies to the single following character. \123 is a four-character escape sequence, \u1234 is a six-character sequence and \U12345678 is a ten-character sequence! (And Python is not the only language that recognizes long escape sequences.)
So in this case, while the current escape sequence is \<newline>, the new proposed one is
Or writing this in the style used in the python docs:
"\" whitespace-other-than-newline * [ "#" anything-but-newline * ] newline
I understand if you disagree with the proposal. But I don't think an argument that it is fundamentally ill-defined and ignorant of history is valid.