Basically, Modpacks can't just be put together as a list of dependencies sometimes they need to add or remove things for compatibility between other mods. My suggestion is to make a tag called "Modpack" on the mod portal which is a tag for all the mods which are a list of dependencies and or compatibility changes.
An additional suggestion might be to add a little interface in game to create these mods which would be an add or remove interface to add or remove dependencies from a new mod in your own library. It would be up to the player to add compatibility changes and upload it to the portal perhaps in game or on the browser.
Modpack Category
Re: Modpack Category
Sounds like a good idea to me. I added the Mod Pack category/tag. Don't expect any game interface from me though :)
ovo