You seem to be using a very narrow definition of "crypto".. I'm not sure whether you're just being pedantic about definitions, in which case you may be correct, or if you're actually disputing the substance of what I'm saying. To answer your question, I'm not a cryptographer, but I have a CS degree and am quite capable of reading and understanding crypto papers (though not of retaining the knowledge for long)... it's been several years since I read the relevant papers, so I might be getting some of the details wrong in how I'm explaining it, but the basic concept of deniable message authentication is something that's well understood by mainstream cryptographers.

You seem to be aware of the existence of OTR, so I'm confused - are you claiming that it doesn't accomplish what it says it does? Or just that something about the way I'm proposing to apply similar technology to this use case would break some of its assumptions? The latter case is entirely possible, as so far I've put a grand total of about 5 minutes thought into it... if that's the case I'd be curious to know what are the relevant assumptions my proposed use case would break?