I have been an advocate of the system of cumulative voting, described here in the Washington Post. The idea is simple — if there are six positions (such as congresscritter or councilcritter) then you get six votes, and you can distribute your votes in any way you choose, including voting six times for the same candidate.
To my mind, such a system is far superior to the district system. In the district system, the districts must first be drawn — usually a partisan process, and a process rife with corruption. The results are a set of winner-take-all elections. Winner-take-all elections require the two-party system that most of us deplore.
But the two-party system is NOT a requirement of the Constitution. Nowhere are congressional districts mentioned in the Constitution. The States are free to set up their election systems as they choose, which includes the possibility of cumulative voting.