I know some may be disappointed, but a united monarchist Germany (or united anti-communist Germany in general) will only be possible if France falls and then is "liberated" by the British and their allies. The reason for this is that France would under no circumstances permit a united Germany, so to circumvent this there needs to be circumstances where the British are able to dominate the post-war agenda in Germany. The only way that could happen is if the French are defeated. With that said, Baden-Wurttemberg will always be able to form a South German Federation encompassing its current lands plus Bavaria.