You might as well rule out everything except Luffy-solo and all of them.
If Oda does an "arc" (note that a two-chapter thing is not really an arc) on one of the characters other than Luffy, he'll have to do one for most, if not all, of the others. Since an arc on each and every straw hat would be ridiculous in length, you might as well rule them all out.
A better prediction would be that Strawhats would meet up in groups and each group would get an arc. Each character getting an arc (which would be what you'd imply if the next arc's gonna be on a non-Luffy character) would not be realistic at all.