Are you guys sure that Rafinha doesn't have what it takes to be a starter? There is no way? I believe he has skills, good technique and mentality. Maybe he can still make it as a AM.
If he dont get injuried again, that is.
As a starter for this season? No, because the likes of Rakitic, Busi, Vidal, Coutinho and even Roberto are ahead of him as they have earned EV's trust. I would say that Arthur has more chances of starting than Rafinha because of his unique playstyle and his price tag.
There's also the issue with formation as EV's favorite position a 4-4-2/4-2-3-1. The double pivot would like be used for Rakitic, Busi, Vidal and Arthur while the Right side of midfield we have Malcolm and Dembele. In this formation Rafinha's role would basically be SS/CAM which is where Messi operates.
Maybe in a 4-3-3, he can be used as an right interior of the 2 attacking midfielders which is his best position but I think EV would go with the other options. I think to be a starter for this season, he would have to show more than the other options that I mentioned or the other players would have to lose their form drastically.
He would be a starter in most teams and he's a really good player, but the competition in Barca is really fierce.