Comments:BIP 0178
Most wallets support BIP32 to allow the user to backup their secrets once and generate multiple keys and receiving addresses from that secret. BIP32 defines a serialization format of the extended private and public keys and uses a 4-byte length "version bytes" (xpub and xprv on the BTC mainnet). There are competing extensions to that serialization format. SLIP-0132 registers extra version bytes that were introduced by the Trezor and the Electrum wallets (ypub, zpub...). Another extension, SLIP-0032 serializes the full derivation path and therefore lets the wallet that imports the extended key detect the used script templates by the purpose part (BIP-0043) of the key derivation. This is made possible, because BIP-0084 uses m/84' as a subtree for P2WPKH scripts and BIP-0049 uses m/49' as a subtree for P2WPKH-nested-in-P2SH scripts.
This BIP-0178 seems to completely ignore that keys are nowadays in a hierarchy and the derivation path determines the script templates. If we assume that each key is independently created, backed up and later restored onto a fresh device, I completely see the purpose of this suggestion. But then I would even extend it with a way to backup a custom script template at the end of the exported WIF together with the private key.
-- Wigy, 2019-05-30