Yes, it's undoubtably technically do-able. The question is whether the development costs and size of the potential market would render it a cost-effective exercise. Like you, I suspect that it may well happen, eventually - but, as usual, I think we'd probably have to suffer a period of the products being extremely expensive before the prices started tumbling.13A RCDs (with a fuse) have got reduced to fit a one gang faceplate. With a deep mounting box, and possibly a somewhat protruding faceplate, I think it should be do-able for either 1 x 20A or 2 x 20A. Of course 2 x 20A doesn't work as well as 1 x 30A for diversity, but if it enables Continental ovens to be wired to British circuits perhaps it's something that needs to be considered.
Kind Regards, John