I think we need to decide if we wish that all panels are of
customizable types (see https://extensions.xwiki.org/xwiki/bin/view/Extension/XAR%20Module%20Specifications#HCurrentFormat), or not.
Also, right now the Panels App UI is offering specific buttons to edit the panels (https://extensions.xwiki.org/xwiki/bin/view/Extension/Panels%20Application#HPanels27shomepage) so we have some inconsistency if we consider that they’re not supposed to be edited.
My POV is that we should expect them to be edited or even deleted and thus be considered
demo pages. This means they’re upgraded when no changes is made to them but as soon as a user makes a modification, they’re not upgraded anymore.