Some suggestions for improving adoption of this:
1. Don't have a dependency on hyprlang. Other projects will probably be averse to that. Use a more common configuration language, using a common library.
2. Have a shim layer so that hyprcursor cursors can be used by applications that use the XCursor API (maybe have a drop in replacement library for libxcursor that delegates to hyprcursor).
3. Have a specification so other implementations can use the cursor format as well, in case other compositors/clients don't like your implementation for some reason.