Ralf, in a video I saw with someone from Alfa Romeo, they said that they had designed it with a spider version in mind. But as far as I know, the first version will be a hard top. Most likely a spider version will follow.
I think some kind of targa or foldable metal roof would be cool. Like the Ferrari 458 Spider or the 575 Super America.
I also like the "humps" behind the seats on the 458 Spider and on the Porsche Boxster Spyder. The Boxster Spyder looks so much cooler than the normal Boxster because of those things.