In the EU there is already a similar system because, in the parliament, the number of MEPs is not really proportional to the population (Germany has 84,48 million inhabitants and 96 MEPs, so 1 every 880,000 people, while Malta has 553,000 people and 6 MEPs so 1 MEP every 92,000 people).

The difference is MEPs are appointed proportionally within each state (so if a party gets 40% in a state, it will get ca. 40% of the state's MEPs)