The SoulBounds EIP proposes a standard interface, called SoulBounds, that extends the ERC-1155 token standard to support the representation and management of soulbound assets on the Ethereum network. Soulbound assets are unique digital items that are permanently bound to a specific user or address, preventing transferability to other addresses.
Regarding the soulbind and soulunbind functions, other token standards omit functions which are only likely to be called by the deployer of the contract. For example, ERC-1155 does not specify a mint or burn function. I’d recommend not including the soulbind and soulunbind functions because they aren’t likely to be used by most people interacting with the contract. Further, some contracts may not even support unbinding tokens, so that function will be entirely useless for them.
Bit of bikeshedding, but have you considered soulOf as an alternative to soulboundOf?