If I understand correctly, some old punch card machines had a backspace to make overriding values on a punch tape possible. This feature would be nice as there doesn't seem to be any use for the backspace key at the moment.

The old tape punch machines did not have a 'backspace' you cant 'un punch' the hole.
if anything the backspace should go back and punch all spots in the previous spot.

from https://wiki.c2.com/?PaperTape
The code of the control character DEL is all ones (except the parity thatis, as usual, unspecified). This is a tradition from the old days of computing (and also from telegraphy), when punched paper tape was an important medium for input/output. When punching information on a paper tape, whenever the user noticed an error, they would delete the bad character by pressing the DEL key on the keyboard. This worked by backspacing the tape and punching a frame of all 1's on top of the holes of the bad character. When reading the tape, the tape reader would simply skip any frame of all 1's.

Im not sure if the sequencers should automatically skip over any 'deleted' symbols as in redstone mode we would lose the max output strength on the black (i think) wire. It would be fine if the other blocks ignore the deleted character