So your saying he can be a xavi replacement (Not ability type-wise) and be a deeper-lying playmaker?
Not exactly, I'm just saying that he's a player who drives forward from deep and will track back in defense. He's definitely attack minded (although still good at maintaining possession) but he's not the type of midfielder who only roams forward and thus opens us up defensively. This is great for him since it means he has the option to play alongside Cesc or Iniesta in midfield instead of just battling the two of them for playing time in one spot.
We'll assume 4 main rotation midfielders next year in Xavi, Iniesta, Cesc, and Rafinha (I think Roberto has to be fringed for players of this quality). Since Rafinha has a uniqueness about him and versatility in where/how he plays, he could assume a number of different roles. He'd be the playmaking attacker driving forward when playing alongside Xavi or even Iniesta. With Cesc he'd be a quality linkup player. His style allows him to not be a liability regardless of who his partner is, so there are more situations where playing him is an option and thus he gets more time (especially with Xavi's age).
If he continues this way at Celta Vigo, it's almost guaranteed that he'll perform well at Barca (since his teammates here would provide better support). That way he gets to show his abilities in a team that services him better and he doesn't have too much pressure on him to lead. This gives him a chance to assume more responsibility as he pleases when he gets more comfortable.