The Papacy is omitted because, let's face it, most of those who wish there were still a King of France and a Holy Roman Emperor probably also wish the Holy See had a different occupant at present, and it's impossible to imagine the current one ruling the old Papal States. Smaller states are omitted as there would presumably be a lot more than just Luxembourg, Liechtenstein, and Monaco.

The "Imperial Commonwealth" is a new entity distinct from the Holy Roman Empire (whose own modern borders would be roughly those of Germany, Austria, and the Czech lands, with Belgium, Luxembourg, and Slovenia eligible to join if desired), modeled on the [British] Commonwealth of Nations, and meant to include the present states of Austria (including South Tyrol), the Czech lands, Slovakia, Hungary, Slovenia (including Trieste), Croatia, possibly Bosnia, and perhaps also the old Kingdom of Galicia & Lodomeria if detached from what is now Poland & Ukraine, retaining their separate parliaments and prime ministers but sharing the Habsburg Emperor as head of state. The ancient titles of King of Bohemia and King of Hungary would be retained, with the Emperor being also King of Austria, King of Slovakia, Grand Duke of Slovenia, and King of Croatia, an admittedly unprecedented arrangement designed to reflect modern realities as much as possible.