Not to mention sales of a 1/72 Wilhelm Bauer would be extremely poor. Even if that was the only XXI in 1/72 they ever released, I still would have zero interest. Too much conversion work. I cannot imagine them investing the resources into something that no one wants.
One thing that is telling about their email, is that they consider there to be only three popular subs, the VII, IX and XXI. So I doubt we'll ever see anything like a Type X or XIV from Revell. Unless some other company releases the kits, and Revell picks up the molds, as they did from Tehnoart with the Type IXC and IXC/40.
But back to their 1/72 Type XXI. If it is indeed a wartime version I will be totally onboard with supporting their investment..