Is your feature request related to a problem? Please describe.
Probably yes.
We are preparing an in-game convention event in which the MTR mod has been requested. We have a functional modpack updating mechanism to allow us updating the mod list on the fly; however, we have to host/mirror the actual mod files because more than half of the mods used are built from the source. Having a mod with size of ~50 MB may be a challenge for both of us event organizers and visiting players.

Describe the solution you'd like
Provide download options of

• A "server-only" jar where there is no assets/ directory inside it. Possibly also exclude the data/ directory?
• A standalone resourcepack that includes the missing assets/ (and possibly data/) directory, complementing the "server-only" jar. It should also be possible to use a customized resourcepack where only bare minimal resources are present, say, only one type of train is included, just for demo purpose.

The default download should still be the monolith jar.

Additional Information
An example of mod using this approach is The Betweenland mod. You can find a "server-only" version of the mod listed under "[a]dditional [f]iles" section.

@3TUSK This is a good idea. #392 adds server-only builds. You may access those via the artifacts of each run. I can also post them on CurseForge when I finish the new release.