[Gesta Bellica]

Hmm i'm not sure what kind of answer you expect because you asked about Italy but then you talked about European federalism, but i'll try to answer to both points

Well first of all I think that every nation bordering with Northern Italy has already a strong identity and i don't see so many similarities, if not with Southern France's culture and language.
Northern Italy for me is Valle D'Aosta, Piemonte, Liguria, Lombardia, Trentino, veneto and Friuli, that's it...
I don't know how the rest of Italy should reconfigure after an hypothetical Nothern secession and honestly i don't care that much, it's none of my business anyway.
It's just exactly because "no one single model serves for all regions/countries/nations in Europe" that i really don't feel like considering an European federalism with strong ties..for me is merely a system of co-operation but with indipendent governments, just like the old European Union used to be before they decided to let us buy their greedy theories about open borders and the like...
In this new/old model every European country should feel free to partecipate, Southern Italy, Russia, Spain, Iceland..i would not take this new federation as an union composed solely by nations tied with strong cultural/genetical similarities but more like a common front against non-European influences