With a copyright assignment, the authors could take the entire project closed-source for future versions. You'd still be able to use older, AGPL-licensed versions, but perhaps not newer versions.

For programs like this, I see little benefit of AGPL over GPL, since the main use-case will be in-house deployments. I can't see how anyone would deploy something like this on the backend, where if you made an in house-fork with bug fixes to support your proprietary infrastructure, you'd have to publish the patches for the wider community. It seems like a big red flag to me.