I think one common instance for all Wikimedia wikis would be more user friendly, though I don’t know if it’s possible to keep up with the edit streams of all wikis at once.

The Wikimedia event stream sends events about all wikis by default. Given that Wikidata is the wiki with the highest bot activity by far (I think?), I am not too worried about the scalability of the listener if we add interested wikis gradually. There is also room for optimization in the listener, which I have not done: Wikidata's own rate-limiting is enough to keep the tool running at the moment.

But it probably requires more work to adapt the models / UI / API to support multiple sites.

It's also worth pondering whether we really want to invest in this particular external tool or if it would be doable to have that as a MediaWiki extension (T203557). It is clearly more involved, but it would probably be healthier.

My own motivation to work on this tool was to enable Wikidata editing from OpenRefine (I did not want to launch a mass-editing tool without having a mass-revert possibility). I do not have plans to dedicate significant development efforts on this tool in the foreseeable future beyond that particular need (so, basic maintenance to keep the lights on, such as #23). My intuition is that me working as a volunteer on this would lower the priority for WMF/WMDE to tackle this problem themselves in MediaWiki, which is not really helpful on the long term. (I hope this makes sense?)

That being said there might be good reasons why the foundation would actually oppose implementing something like this themselves. In that case, an external tool will remain necessary and as a maintainer I would try to grow the contributor community and make the project sustainable as such - which again might involve stepping back a bit from development itself.

So I think the deployment of Structured Data on Commons is a good opportunity to have that conversation, to understand a bit better what is the stance of WMF/WMDE on this on the long term.

Given that we are working on support for Structured Data on Commons in the OpenRefine project, we need to be able to revert batches on Commons. Therefore I will run an instance of EditGroups for Commons. The concerns above still apply: it should just be treated as a temporary solution until there is proper support for that on MediaWiki's side.