Sure, it's workable but how people would feel about it is another question. It would probably transpire that the countries of Wales and NI would both map direct

Sure, it's workable but how people would feel about it is another question. It would probably transpire that the countries of Wales and NI would both map directly to states with the same names (with powers). You then have a country of England (with no powers) broken into constituent states (with powers) and the whole thing starts to look like a CGP grey video. Historically, Germany is quite different to the UK for obvious reasons. I also suspect Scotland , Wales etc would be more likely to table flip when dealing with a UK parliament than say Saxony would.