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The whole purpose of the key= argument was to avoid having
to build (key, record) tuples.  If those are going to be
built anyway, then there is little point to using key=.

Closing this because:
1) the original use case was better addressed through other
methods
2) key= for bisect does not provide the same benefits as it
does for other functions.
3) the most recent proposed use is far afield from what key=
is supposed to do
4) I think it is bad design and would encourage misguided
approaches.