"Have You Considered?"

Have you considered limiting drive spinup?

Yes. See Limiting Drive Spinup.

Have you considered porting to MacOS?

Yes, but the FUSE implementation on MacOS has gotten a bit complicated and fragmented. I'm not opposed to supporting it but given the low demand, lack of the author having a modern MacOS system, the fact mergerfs does not use standard libfuse API, and MacOS FUSE situation it is unlikely.

Have you considered porting mergerfs to Windows (WinFsp)?

Similar to MacOS the demand is very low and mergerfs does not use the libfuse library so porting to WinFsp would first mean porting it to libfuse.