1. "This patch adds too many lines of code and not enough value."
If the maintainers judge it so, I have nothing to say. You have the responsibility to keep the codebase relatively simple.

2a. "Existing programs made with the assumption that repr(row) is short (albeit useless) will break when it becomes not so short."
I have no experience maintaining popular language implementations, so I defer to your judgement on what level of backward compatibility is warranted.

2b. "New users of new repr(row) will run into problems because its size is unbounded."
I think this objection is invalid, as I explained in the comment: https://bugs.python.org/issue35889#msg336291