I'm working on a mod that adds the concept of tool materials, and I'd like to be able to load their properties from data packs. Right now, Minecraft has a hardcoded list of DataLoaders, which makes doing so hard. It would be easier to do if Fabric provided a way to register our own DataLoaders (or more precisely, functions to generate them per Server) and sync its data to the client if requested.

Fabric API has a class called ResourceManagerHelper for registering ResourceReloadListeners for resource pack / data pack loading.

Thanks, that was what I was looking for.