We don't have a plan for this yet.

Perhaps a different namespace?

It could make sense to have them integrated with the Wikibase registry

We probably need some sort of slightly automated discovery? but probably don't need to list them on the registry.
If you know where wikibase is you should be able to get the shex.

There are some circumstances where a shex user doesn't know where the wikibase(s) are, e.g. when treating shex as interfaces in order to build consumer tools.

Just wondering if this can be closed in the eyes of WikiProject-ShEx now that we have the sex mediawiki extension?

@Addshore Good question. It makes sense to store those schemas on the ShEx extension. I would benefit federation and findability. However, the current extension uses the WDQS alone, so it would difficult if not impossible to use a shex on given wikibase data.

In T192920#5276590, @Andrawaag wrote:

However, the current extension uses the WDQS alone, so it would difficult if not impossible to use a shex on given wikibase data.

So, the current extension is configurable, using the wgEntitySchemaShExSimpleUrl setting.
In WMF production for wikidata this is set to:

https://tools.wmflabs.org/shex-simple/wikidata/packages/shex-webapp/doc/shex-simple.html?data=Endpoint:%20https://query.wikidata.org/sparql&hideData&manifest=[]&textMapIsSparqlQuery

For a custom install this can be configured to point at the hosted shex-simple app on tools with a custom Endpoint, or even to a custom install of the shex-simple tool.

I think it makes sense to close this. Issue. As @Addshore suggests, with the extension being available to any wikibase. it is done.