The identification and classification of migrants is not going well in Italy, Greece, Malta or the Balkans. The EU Dublin Convention, now known as the Dublin III Regulation, states EU (and some other European countries') rules for identifying migrants. Avoiding and evading this identification is a primary goal of migrants to Europe as it determines rights to place of settlement, or even settlement at all. Taken to reception centres on the European mainland after rescue in the Mediterranean, the migrants run away as fast as they can once they've grabbed a change of clothes and a meal.
The proposal of an Ellis Island was always waiting but has been precipitated by the closing of nation state borders to migrants, shutting them off from their settlement objectives, and rendering transit countries' city public spaces, transit hubs, and countryside bordering migrant routes simply squalid. None of the Mediterranean EU member-states is noted for bureaucratic efficiency and some are plagued by corrupt bureaucratic practices. Their islands are particularly lovely, often set in national parks and areas of outstanding natural beauty (even those that have served as penal colonies in the past; not a happy association for a migrant reception and identification centre). Pianosa, 13 kilometres off Elba is all of these things. As such it shouldn't even be contemplated for reception centre use. The suggestion of Pianosa made in the Corriere della Sera is presumably just a way of getting the policy ball rolling.
So where (see list) should Europe have its Ellis Island, to meet its own Regulations and end the hurried piecemeal imposition (with all its appalling side-effects) of checks here and there across the continent?