It could be useful to have an API that you mention. But the question is what does "element content" mean in the spec, and we definitely should have an API to support encryption (and of course decryption) of that "element content".
At the moment, the API exists - but it assumes you want to encrypt all the children of the passed in element. That's probably not enough in the long term, but interested in all thoughts!
Cheers,
Berin