@swick@siosm@adamw@garrett@notting I would suggest this only when a flatpak app is installed or uninstalled, thus the "source" and "target" language I used. (You might reasonably also suggest a separate capability for users to choose to initiate this at any time if they so desire, but that's not part of what I have been suggesting.)
If the config doesn't make sense to copy for some particular app, then it would be a bug to declare such an equivalence using this suggested feature. But this is not a normal case.
It is not complexly specified, so complexity would be an unnecessary aspect of implementation.
Calling this "little gain" and crudely dismissing it is discouragingly dismissive, and devalues the work that users have done in developing their preferred configuration. ☹️
If it were declared, then at the very least, users could get information in a consistent way about how to preserve their configuration, and not have to hope that they found the right stack overflow answer when they do a web search. The question of whether to automate copying could reasonably be a separate conversation from making a consistent record of equivalent paths for configuration. But the possibility of such a feature could add rationale for implementing the record in the first place.