What's the "Vila arc" ?
Well, Vila was mentioned three times.
First, when Nami read bout it in the newspaper b4 they were headin to logue town (there was a rebellion goin on @ Vila).
Second, when Noland mentioned it in his log book (in Noland's time Vila was a happy place).
Third time, when Oda told bout Vila in som SBS, he stated that Vila was a country almost as big as Arabasta and that tourists aren't welcome there.
Of course, all this facts don't have anything to do if the SHs will get to that island, but it'd be bad to hype sth that much and then don't bring it into the main story. The islands around W7 are a different story (St. Popura, San Fardo and Pucci) haven't been as hyped as Vila.
And dont forget the Vegapunk arc! Both Chopper and Franky will have some good conversation with that Doc!
Also there are @ least two arcs where Chopper and Robin will leave the crew a short time to get their chapters when coming back 2 the crew (fifth and sixth person).