Napoli have fallen far behind so it will probably not be possible for them to get back into a good position again this time. The way Inter are playing makes it much easier for them to become champions. Inter are ahead of the other teams on points, so it will be very challenging for the other teams to overtake them. Napoli didn't focus on their performance early on which is why they are in the situation they are now. So I can't consider Napoli as likely to do anything good ever
Napoli is 11 points behind Inter Milan and that can easily change to 14 points if Napoli wins Lazio later today. Napoli has not been able to have 3 consecutive wins in the league this season. They've only managed back-to-back wins twice. That's inconsistent. I don't see them winning the league but they can battle for the top 4 spot.
I don't think any team is shaking Inter Milan off that top spot. Juventus seem to be the only contender but even they are not doing enough. They couldn't win yesterday to put pressure on Inter.
If Inter wins today and they most likely will, they'll be 4 points or so above Juventus.