This morning, Bitcoin Core was hanging. I killed it, restarted it, and it took forever to load the wallet (which had grown to 2.2 GB during the rescan).
FYI, Bitcoin Core load whole wallet to RAM which may be reason of long loading time[1].
I think that the number is bigger, since some have posted them as images which you could not "scan".
My list is indeed not complete. I didn't search for Hex keys either, only WIF.
And with HEX, i expect you'll receive many false positive since 64 character HEX also mentioned as hash of a file, as block hash, as TXID or explaining SHA-256.
[1]
https://bitcointalk.org/index.php?topic=5400538.msg60252176#msg60252176