Right now one of the ways we fetch change data - and only one available outside WMF production servers - is using recentchanges API. However, currently there is no support in this API for fetching only updates that relate to structured data - all edits to Commons File: space look the same to it, even though most of them aren't related to SDC data and thus are useless for SDC Query engine to fetch and process. It would be nice to have some mechanism that allows only fetch SDC-related changes. Unfortunately, right now the only thing that distinguishes them is comments like /* wbsetlabel-add:1|en */ but these would be expensive to parse and impossible to pre-filter on API level.
Maybe if we could tag such changes or select changes by slot, it would solve the issue.