This is essentially just CalDAV[1], no? So a FUSE CalDAV client. Surely not that difficult in Go, Rust or something similar with ready libraries.
I reckon, yeah.
From this article[1] writing a FUSE filesystem doesn't look that hard.
I might give it a go this weekend. Assuming I remember!
[1] https://blog.trieoflogs.com/2021-05-25-fuse-filesystem-go/