Bitcoin and many of its altcoin forks have defined the following two variables that specify the first four characters of BIP32 extended private and public keys that are frequently base58check encoded:
EXT_SECRET_KEY (0x04)(0x88)(0xAD)(0xE4) - which maps to the xprv prefix
EXT_PUBLIC_KEY (0x04)(0x88)(0xB2)(0x1E) - which maps to the xpub prefix
BIP 32 secp256k1-based technology for synthesizing extended public keys can't in its current form be extended to synthesizing xpub keys for Ed25519, see Is BIP32 Technology Cryptographic Curve Aggnostic. Hence currently specifying EXT_PUBLIC_KEY values for Monero makes little sense. However, having the ability to deterministically specify EXT_SECRET_KEY still has considerable value.
Here are two candidate BIP 32 related Monero EXT_SECRET_KEY (extended secret key) prefixes to use as base58check extended prefixes for seeds:
1) msec => (0x03)(0xa4)(0xf9)(0x5c) = 61143388 base10
2) mprv => (0x03)(0xa3)(0xf9)(0x88) = 61077896 base10
What EXT_SECRET_KEY will the core Monero Team choose?