On odd years, leagues of (say) 16 formed by ranking all the players ranked in order (perhaps by Elo from chess) and choosing segments of 16. Play round robin within each league.
On even years, the top league is 8 and does double round robin offering more rigorous competition among the very top, perhaps establishing who is the best. The lower leagues remain 16, so the boundaries are staggered compared to odd years.
One could do promotion and relegation, or simply rerank all players at the end of each season (Elo), and reassign to leagues.
How much cooperation and Elo manipulation can occur to game the system? Fischer criticized round robin tournaments.