For Kleopatra I've needed a replacement for the unique KDBusService from KDBusAddons because we want to ship Kleopatra without DBus on Windows.

The requirement was generic argument passing and return value passing. Ideally also without a Socket because this requires the QtNetwork module or platform specific code.

Imo it should match the API of KDBusService (in contrast to QUniqueApplication from qt-solutions) and would be placed in KCoreAddons.

In D927 I've implemented this specifically for Windows but the wish in the discussion of this change was for a solution that would also work on other platforms. I think some file system / lock file / file watcher implementation could work reliably.