Even though the SequenceMode plugin was designed for Annotorious v2, it looks like it still works with v3 - at least on the basis of purely anecdotal evidence: I successfully integrated it in an OpenSeadragon viewer for IIIF with Annotorious v3. I did make a couple of changes, but largely because the platform I am creating it for (MediaWiki v1.39) does not support ES6 syntax such as import/export. The transpiled ES5 version I created works fine as far as I can tell.

Unless the plugin's functionality will be integrated, which would be another option, can we find more @testers and if everything checks out, add SequenceMode to the list of plugins?