The Twitch launcher will happily install the Fabric version when it's the latest version.

As a Modpack builder I have no easy way of knowing that this project support both Forge and Fabric.

Personally I think this is a bad idea. The problem lies within how poorly CurseForge handels things.
As Overwolf have recently acquired CurseForge, hopefully they'll start to fix some of the issues the site has.

Fair enough, sounds like a Will Not Fix / CurseForge's Issue.

That's fine. Just letting you know anyone who uses CurseForge API to keep their modpack up to date is screwed when mod's keep both Fabric and Forge Version in the same CurseForge Project. I can no longer trust that running an update will give me the latest version of that mod.

@nmarshall23 I've been making sure to mark all Fabric versions as 'beta' rather than 'release.' Does that not affect anything? I was hoping it would.