We have recently added StreamTypeErased to make toString()/toByteArray() SCARY (QTBUG-130701). It's also used in the new tuple streaming operator. It might make sense to use that technique for QDbusArgument stream operators, too, also for all (homogeneous, heterogenous) containers  (incl. product and sum types like optional, variant, pair, tuple) to reduce the code size of these calls.