Diego would fit perfectly in Inter. Inter do need a link between the hard working midfield and the attack. They have great full backs, and the only thing Inter are missing is a good trequartista, with good vision. If Inter buy Diego and a top class target man (to replace Stankovic and the forward that plays next to Ibra), then they will be complete and super strong on every single position.
As for us, i can say that i'm 100% pro-Diego and i do think that Ranieri will change the system if we buy Diego.
But i fear that with Ranieri in charge, this would really hurt Giovinco. If Ranieri chooses 4-3-1-2 then no way he'll play Giovinco in the midfield trio. He'll either use 3 DMCs as Inter does or he'll play Camoranesi and 2 DMCs in midfield.
If he chooses 4-3-2-1 then he might use Giovinco and Diego as AMCs, but i don't see him dropping Del Piero out of the team. The best solution will be a 4-3-2-1, rotating Gio, Diego and Del Piero.
But add to this that we'll need top full-backs , who can attack as well as defend, to play 4-3-2-1 or 4-3-1-2, and you'll realize that Diego alone means nothing. We still need to seriously improve the defense, especially the full back positions.