Fiorentina always treat the EL/UEFA cup seriously (they reached the semi-finals in 2008) so I can see them try to win it, and they have the squad to do it. Benitez usually tries to win the EL but De Laurentiis doesn't seem to give a shit about it so we can't expect much from Napoli. Lazio is a mess at the moment so count them out as well. We should be able to win this if we take it seriously.
So, a Juve-Fiorentina final is potentially in the making
I still haven't forgiven Fiorentina for the semi-final failure in 08, even though everything worked out in the end.
Anyway, I think how the league goes between now and the spring will decided how seriously the teams take it.
Juve aren't going to risk not winning Serie A, so they probably need to have a decent lead in it before they'll really go for it (though Juve have the depth to see off a fair amount of teams while resting some players).
I doubt Fiorentina will risk missing out on a CL spot to focus on the EL (if it this year or next year that the rule change allowing the EL winners into the CL comes into force?), so they are the team I'd see least likely to really commit, as they'll probably be in a battle for the last CL spot.
Napoli are the ones that there may be the biggest chance of really having a go. I could see them, but the spring time, being several points behind Juve, but several points ahead of anyone else. That would give them the opportunity to focus more on the EL, and Benitez's record shows he will be inclined to try and win it if circumstances allow.
Lazio could be dangerous simply because they may well have nothing else to play for come the spring. No guarantee they'll still be a mess by then, but they may well be far enough behind in Serie A the the cups get almost their entire attention.