I think you misunderstood Grey Wolf.
He doesn't in any way say that MitD can't be iconic (or must be DnD), but that it doesn't need to be iconic (whatever that means). The iconic-ness or DnD-ness or the coolness isn't relevant for a monster to fulfill the requirements for being MitD.
If you think that a iconic non-DnD monster is a good fit, just propose it and say why you think it could be MitD. But saying "it should be iconic" doesn't help. We don't know whether or not MitD is iconic or not (or DnD or not DnD; or cool or not).