I agree: while it is not likely that the alternate state functionality will break the extension might very well break in a future Qlik Sense release, even if it only uses the published APIs. Somebody needs to take responsibility for the extension, before upgrading your Qlik Sense installation you need to verify that the extension works with the new version and posibly not upgrade if it doesn't.
I was looking for alternate states implementation but with no extension requirement.
I figured one based on data Island.
Was going to build an example but it's already done on community.
In any case it's still sth you're looking fore here it is: