True, but the discussion is here veering towards state actors, and they could indeed use the diplomatic channels with gay abandon.
As for Assange™, I believe that ploy failed because he had to be first accepted as a courier, and that didn't fly (and thus neither did he) for obvious reasons. Ditto for ideas of making him a diplomat.
Speaking of which, he's been miraculously quiet of late. Is that because he still hasn't got his Internet back, or are Trump and Brexit absorbing all the publicity oxygen?