To catch Inter Milan, I feel it is almost impossible at the moment, considering their extraordinary performance, unless Inter Milan suffers from the bad luck of having to lose repeatedly, that might open up opportunities for AC Milan or Juventus to catch up, and even then They (AC Milan and Juventus) must be consistent with the wins they must achieve, because if not, it would be the same as lying even though Inter Milan repeatedly loses.
For the top 4 positions, maybe they will be able to do that, but of course with a note too, they have to be very good at winning every match they play, both away and at home. Consistency is the main key that will lead to the Champions League next season.
Six point ahead staying at the top of the table means that you will have to win three straight matches and the team at the top will aswell have to loose three straight matches too then you will be equal with them and maybe using goal difference could displace them but I don't see that actually happening with inter Milan at this point neither do I see AC Milan been able to pull up such at inter Milan at this time of the league.
Juventus has sadly fallen behind enough not to even think of been able to catch up with inter Milan and getting ahead of them thereafter. I don't see that consistency in winning with either AC Milan or even Juventus, I doubt if they can at this time get a straight four wins in a row which will now give them an edge at inter Milan,. moreover inter Milan isn't even at the point where they would want to be loosing that much to give AC Milan and Juventus such opportunity so it's more like both teams (Juventus and AC Milan) will just compete within themselves.
Either of AC Milan and Juventus can finish at the second position but they are both finishing at top four which isn't much of a bad way to have ended the season but a considerable fair one. Juventus can hope to improve and get another opportunity next season, the opportunity they got this season was actually messed up after they lost to inter Milan a d since them they have been unable to recover again.