[1] not sure which prefix though, 1, 2, 3, 5 are used, so maybe 4? or S for SegWit?
It depends on SegWit program. I think it will be p... for P2WPKH address and 7... for a P2WSH address.
But it looks that BIPs change on the go.
BIP142:
For P2WPKH address, the address version is 6 (0x06) for a main-network address or 3 (0x03) for a testnet address.
For P2WSH address, the address version is 10 (0x0A) for a main-network address or 40 (0x28) for a testnet address.