There isn‘t much at the moment that requires Simconnect. FSUIPC does, I think Simlink (Navigraph charts) does, maybe some features of the Flybywire A320 mod, IDK. But in the future addons will definitely require Simconnect. Everything that runs outside of the sim environment and needs to interact with the sim will require it. Accusim for example, external EFBs or FMC devices, etc…