SUMMARY

Migrating from one system to another would be way easier, if KDE featured an option to export the configuration of the current system settings. Obviously, this should not include hardware-specific configurations like network or sound configuration and security-relevant configurations like the firewall (though these might be optional via opt-in).

This export feature should include all settings but the following:
   - Users (obviously)
   - KDE-password-storage (optional)
   - online-access (optional)
   - backups (optional?)
   - all settings of the network category (though e.g. firewall might be optional)
   - everything of the hardware-category (though energy-settings might be optional)
   - software updates (might be a security / stability issue?)

Every option remaining should be de-selectable or selectable, if only partial exports are wanted.
Selected themes should either be included as a link to the theme that's then downloaded or optionally directly in the export-file, without the need to download it (might be useful if themes are not available anymore)

It might also be worth a thought if every KDE program should include such an option, saving all exports in one specific location, making it possible to export the configuration of the system and the used programs, that's ones imported on another system (recognizing, which settings config belongs to which program) and applying the configuration once making a new installation of a highly customized system way easier.
This approach also spreads the responsibility for this feature, so that plasma's system settings doesn't have to include the export logic for all KDE programs, but every application is responsible on it's own. Importing settings should also be handled on a per-application level, so that system settings would only forward the to-be-imported settings to the application, which itself applies the settings (so that system settings only works like a "hub" connecting the config export-and-import functionality of the applications, only calling them to export their config or import it, though it might be smarter if the export is handled actually on a per-application-level and only the import is triggered on one place of the system.

This could also include the feature on supported systems to install applications, which have a config file to be restored that's not installed on the system, making the configuration of a new system even faster, maybe including an option to export a list of installed applications that should be exported as well.

Settings that potentially include personal information should be disabled by default.