Is this information still current? This post appears to be from 2014. https://2sxc.org/en/docs/how-to-create-your-own-app
I searched in here but didn't find anything relevant, but sometimes its easy to miss an obvious key search term. https://docs.2sxc.org/
Also, is it still on the roadmap to allow "apps" to be upgraded to newer versions? I realize that gets complex, especially in the case of the Content-App.
This is still correct AFAIK.
App-Updates have been improved with view/content-type etc. import-export but there is currently no direct compare-feature or something yet, and we won't be able to develop something like this in the next few months as other priorities must come first (Oqtane support, a big VisualQuery release, a big Metadata-Release, etc.)