Could this be uploaded to Modrinth? It is one of the only mods in my pack that isn't on Modrinth so an upload there would be awesome! If a Modrinth release isn't planned, is it okay to distribute your jars in my pack (the actual jar file, not a link)?

I guess this issue can be closed now: https://modrinth.com/mod/ender-storage

Correct, the mods are now dual released on Modrinth.