Why don't they just use Morer as Palencia's back-up? Are we getting rid of Morer to make room for this kid? Unless he is regarded as one of the best talents in his generation, there is no point of signing young players from outside and remove our own product.
I think we should bring talented players from the outside and let our kids compete with them. If Morer is better then he'll play, if this kid will be better then it's his turn. You can never have enough talented players and we shouldn't look at everyone we brought from the outside as if we are trying to get rid of our youngsters but rather as a competition for them to eventually make all of them better.
I don't think either Trapaga or Morer will be in Barça B next season though as there is still Nili as a backup to Palencia. As said above he'll most likely go on loan (possibly to Segunda B team to get some experience in senior football as he so far has only played for Villarreal youth teams) and then maybe return next year when we'll probably have to replace both Palencia (he could be promoted to the first team or loaned) and Nili. So I think this is more a longterm signing for B team with potential to make it into first team (probably not very likely but it could happen). Just looking at that video I think he has talent so nothing wrong with signing him for free and see how he'll develop.
With Palencia, Morer, Trapaga and Morey we have some talented RBs and let's hope at least one of them can make it into first team in the future.