To be honest, I haven't received any official news about the players they will recruit next season. Juventus and AC Milan are indeed tough competitors for Inter Milan for next season. I can say that this season Juventus and AC Milan cannot put pressure on Inter Milan who dominate Serie A. But if they are active in the transfer market this season I think they will really be a tough competitor for Inter Milan.
I don't know how AS Roma and Napoli will fare next season. As Roma will be better next season because I see De Rossi is a great coach. Napoli performed very badly this season. I'm not sure they will be contenders for the Serie A title next season.
I think that Napoli has a chance with Conte, it looks like he wants to keep all the key players and bring in some of the other teams, so there is optimism about Napoli, but for Juventus I can’t say the same, I’m not even sure how good Motta is for Juventus. I also don’t see them actively working on the transfer market, so I think they will fighting for a place in the Champions League, but nothing more. And I agree that it will be difficult to compete with Inter, they have retained the team and can repeat their success again.