Twitch modpacks cannot include projects that aren't on Curse, and that includes unreleased versions of projects that are on Curse. The latest version available on Curse is 4.9.1.92 while the latest version is 4.9.2.1 available on the Maven repo as well as precompiled by another GitHub user in #1461 . For everyone wanting to use Mechanical and the Betweenlands, without asking their users to download individual jars separately (which many server owners will not do), this is a problem.

v4.9.3 sprint ends this weekend. Will have a release on curse.