In addition to adding OpenSSL switches mentioned here
I would look forward to switches that permit the 'l' literal key and the 's' or 'i' salt/iv parameters to be fed as hex strings.
Where the $lower(L) switch currently accepts a variable length 1-56 UTF8-encoded text string as a key, something like $upper(L) would accept a hex string up to 56x2=112 digits in length. This would be decoded to binary and used as the 1-56 binary length literal key even if it contains byte values 128-255 or 0. This would be different than OpenSSL's -K switch which limits the hex string to 32 digits.
Where the $lower(S) or $lower(I) switch currently accepts 8 text digits as the salt or IV, an $upper(S) or $upper(I) switch would allow defining these as up to 16 hex digits. From what I understand of OpenSSL, these would be pretty much the same as the -S and -iv switches it uses, and would probably be two of the OpenSSL switches mentioned in the other thread.
If l/L and s/S and i/I are considered too similar to each other, perhaps H and h switches as modifiers for 'l' and 'i' or 's'.