My idea would be....keep P&R as it is with the tri-yearly franchises. But you can only get relegated from SL if you have finished bottom of the league. As the original post said 3 divisions of 14. There should be just as strict criteria for promo to the Championship from Ch1 but do this yearly.

Bin Murrayfield magic for a big season opener-start with a bang.
Keep NRC at Blackpool-that works well.

End of season internationals to consolidate and progress, European Nations, Pacific Cup, other Nations playing tests (however minor they are)

Much stricter regulation on Nationalities of players. Choose a nation and stick to it. Once you have represented this nation, you wear that nations badge under your name on your club shirt.

Why not ban overseas players.

Think about what you have just typed.