There are a few problems in this scenario.
The first one is that outside the Savoy there is no other Italian dynasty on the thrones: Lombardy-Venetia are an Austrian province, Modena and Tuscany are governed by Habsburgs, Parma and Two Sicilies by Bourbons. None of these dynasties are supportive of an Italian unification (which is not the real issue: after all the German states too were not in favor of coming under a Prussian supremacy, and still all of them was brought into the empire, mostly at bayonet point), but even more importantly none of these dynasties would be trustworthy. The lessons of the short-lived Customs Unions in the 1840s (only the Papal States, Tuscany and - with some reluctance - Sardinia joined it but it never worked in practice) and even more importantly the betrayal of the idea of a national fight for Italian independence in 1848 (the Papal States were the first to renege, quickly followed by Two Sicilies and finally by Tuscany too) were too vivid in the minds of Italians. Even if the war of 1848 is successful, the end result would simply be an 1859 ante-litteram: Lombardy, Parma, Modena and the Papal Legations had already voted for annexation to Savoy-Piedmont. Even most of the cities in Venetia and Friuli had followed suit, and the only one sticking with a republican system was Venice itself. IMHO Tuscany too might send the grand-duke packing (as they did in 1859) and Venice could not stay aloft forever. In 1859 there was no doubt on the outcome within a couple of weeks from the start of the war.
The second problem (maybe should be the first one) is what to do with the Papal States. It would not be possible to have the pope subordinated to a king of Italy, if only in his role as temporal ruler, and the Papal administration of its territories was by far the worst one in Italy (or I should say in western Europe). Equally unthinkable would be an Italian Federation under the presidency of the pope, as argued by the neo-Guelph in the 1840s: that idea never gained real traction and was dead in the water after the events of 1848-49. In any case it would never have worked as a practical solution.
Finally Piedmont-Sardinia ordainment was patterned on the French one: a centralized state with the provinces controlled by prefects appointed by the central government. In a way it's the smallest of the problems (if there were an alternative system it might have been considered) but the point is that there were no practical alternatives to a centralized state.
A federal state might have been a possible outcome if the popular insurrections of 1848 had been more successful and better coordinated (starting for example with Cattaneo convincing the Provisional Government in Milan to refrain from offering Lombardy to Charles Albert), but the coordination was not there and more importantly the only hope for a successful war against Austria required the willing participation of the Sardinian army. It's not a surprise if the popular insurrections were successful for a limited time only (with the only exception of France): even in Germany the parliament of Frankfurt did not manage to successfully secure the constitutional gains of the beginning, their offer of the German crown to the king of Prussia was unsurprisingly rebuked ("the crown from the gutters") and in the end Prussian troops restored the previous order without too much trouble.