I do believe the French-turned-Habsburg/Tuscan Italy is the most interesting suggested so far, though I could foresee some problems occurring for this Kingdom.
The main one being divisions: geographical, socio-economical, political, etc.
These are very important to address, as it should be noted that the south of the peninsula is often regarded as more rural, with a more industrious north. With that, political divides would likely occur, maybe even communists taking major power in the north due to factory conditions, or republicanism in the south to support the rural Italian voice. All this doesn't even account for the east-west division caused by the Appenine chain.