For both these EIP’s, it’s unclear to me whether or not the extension to the 721/1155 spec need to be part of the underlying 721/1155 contract.
The purpose of this EIP is to create a standard that can be built into the token contract itself, keeping gas costs lower by having fewer external contracts involved.
If so, wouldn’t it be better if the spec were around the ability to add a redemption to a 721 or 1155 in general?
Yes we definitely want to support redemptions across tokens already deployed. This is why we developed a registry-like version of this EIP as SIP-14: Redeemable Contract Offerer that contains both ERC-7496 Dynamic Traits and ERC-7498 NFT Redeemables together. This means that anyone (including non-token owners) who wants to set up a redemption campaign does not need to deploy a new contract, only register the campaign with the Redeemable Contract Offerer which will emit the same events as the EIPs for external apps to pick up and understand.