Also there's no way to encode a sha1 or sha256 message as a base58 address (thus send it to someone to pay you at), because all of the currently defined formats expect ripemd160 hash as input.
True but addresses are more like agreements rather than consensus rules, so technically two parties can come up with an agreement that a certain encoded strings represent certain script types. It's just that we agree that a base58 string that is [0x00 + 20 bytes] represents a P2PKH script, we can simply extend this agreement (whether globally or between two parties) that a base58 string that is [0x01 + 20 bytes] P2PKH with the hash replaced by SHA1.P.S. SHA1 is not safe to use by the way.
