Separately Deployable Engines

Looking for thoughts here, and how to proceed. What we'd like to be able to do is deploy our engines separately from our main application. We have a giant monorepo app that we're working on splitting into engines, but even engines are beholden to the main application to be deployed, causing some pain / delays. We'd like to be able to deploy engines separately to their "mount point" when they've been updated, such that the main application could just pick up the new code, instead of having to update a version in a package.json, or something similar.

Please let me know if there's a better / different way to go about suggesting this.