There are also more short-term implications to the issue of who is named as heir. Nayef, who has been all but officially named, is very conservative and considered to be close to the clergy that 'advise' the Saudi ruler. He's taken a pretty hard stand against the protests of the Arab Spring and as Interior Minisiter, he knows where the bodies are buried and who the 'subversives' are within his country and the ME in general. Some analysts consider it likely that he was the driving force behind sending Saudi troops into Bahrain to 'assist' in keeping order. He's also spoken out against some of the modernizing steps taken by his brother such as allowing women to vote by 2015. Should he accede to the throne, it seems likely that he'll direct and support a return to an even more Sunni-oriented, hard-lined Islamic state.
Nayef is also very anti-Iran and given recent events, naming him as heir will send a message to the Iranian leadership which will undoubtedly increase tensions.
As far as relations with the U.S. are concerned, officially Washington likes him and really likes his son and assistant. But this quote from a WaPo article
gives a different perspective of Nayef's thought process.
"...“Nayef got religion, not after 9/11, but after the two attacks in 2003,” said Alterman. Earlier, Nayef had bristled at questions about the 15 Saudis among the 19 hijackers who struck New York and Washington and about the role of private Saudi money in financing al-Qaeda. And he infuriated some in the United States when he said in a 2002 interview with a Kuwait newspaper: “We still ask ourselves: Who has benefited from Sept. 11 attacks?” adding, in a reference to Jews, “I think they were the protagonists of such attacks.” "
It'll be interesting for the U.S. to have diplomatic relations with a Saudi king who has publicly blamed Israel for the 9/11 attacks.