Thanks for this great post! I like the idea of having one universal design that allows multiple cryptographic solutions.
Can you give a bit more details on the syntax / interface of these two functions? Especially, I think having that spelled out would help to verify if the proposal is really decryption-mechanism agnostic, i.e., supports threshold enc, delay encryption, sealed transactions (?).
Also, I was wondering if you have thought about which security notions (at least informally) the used decryption mechanisms should satisfy (e.g., for threshold enc, there are tons of notions to choose from).