Promise return types

Someone asked me a question recently that made me look more closely at our return types for the subtleCrypto functions. Should we look at tightening these up a bit instead of having them all be Promise<any>?

Specifically, is there any reason to have exportKey and wrapKey return Promise<any> instead of Promise<ArrayBuffer>? The way it's set up now, it would be very tempting for someone adding a future algorithm to, say, return an object for the JWK export instead of serializing it first as all the existing algorithms do. This may develop into a hassle for programmers as they would have to track what each algorithm does for each format.