It would be useful if the published version number of the app was available as a variable within the app. By displaying in a text field, you then have an immediate and dynamic way of seeing if a user is running the latest version.
Updating status and adding @GregLi
Totally agree. See my idea about extending the App signal to include AppId, WebLink, SessionId, as well as InterpreterVersion (which I think is what you're looking for).
Also note that it is possible to use an MS Flow to get this information. You'll need to create a Flow with a PowerApps trigger. In the Flow you'll pull out the request body that was sent to it, and parse it for:
There's also a ton of additional information there like user ID (in x-ms-username, x-ms-user-name-encoded, x-ms-user-email, etc.).
Hope this helps if you need this info in the meantime.
If you are at it: also make the last saved version available (in case the PowerApps has been saved a bunch of times but not published yet).