Why do you have so great expectations on Pedro Sánchez? He's just been elected as party leader and it seems that socialists are not gaining traction at all.
He's young, charismatic, and not seen as a professional politician. He promises a lot of big things, including difficult ones (federalization of Spain for example). I think he's going to become very popular soon because he represents the change that so many want to see. These days I think that's enough to win in countries like Italy, Spain or Greece.
Like Renzi, if elected he will have to prove himself because many will see as a good communicator only.
I don't think he's a good communicator, and it's very unlikely he'll bee our next President. And I say this as a member of the PSOE
(who supported Edu Madina).