Clearly the next step after S is to flip it on its side and make it infinite.
A "summer" update for Nintendo Switch Sports is coming soon.
The free update will release July 26/27 (Tuesday night/Wednesday morning) and will include expanded support for the Leg Strap accessory in soccer matches (4v4 and 1v1), plus new volleyball moves. Post-update, volleyball will include new "Slide Attack" and "Rocket Serve" moves.
New tiers for the online leagues will be added, known as S Tier and ∞ Tier. It will also be possible to create rooms for matches outside of the friends list.