Nothing. Obama, now he gets into the history books. The lefties, who write the history books, run the schools, and control the MSM, love the idea. They will give it a good press, possible for the next fifty years. So Obama did it for him, not for the country.
Diplomatic recognition is desperately important to the Castro regime. It means the Americans will give up attempts at regime change, something that we have tried in the past. Rumor has it the CIA tried to kill Fidel with a poison laden cigar back in the day. Now, with embassies established in Havana and Washington, all the Cuban have to fear is nasty diplomatic notes, rather than a second Bay of Pigs.
Charles Krauthammer groused that Obama gave the Castros diplomatic recognition with out demanding any concessions from the Cubans in return. He has a point. On the other hand, what concessions, short of shutting down the communist police state, do the Cubans have to make? They are broke, their people barely have enough to eat, they lack natural resources, they have nothing worthwhile to export save cigars.
So Obama, grabbing for his place in the history books, hands the Castros a fantastic bennie.