Seems bit strange to me that McLaren seem to be Alonso's target rather than a potential swap with Vettel. Red Bull have just promoted from their young driver programme with Daniel, so it's not like they should feel compelled to go down that route again should Vettel leave, so why McLaren?
It's extremely unlikely the McLaren-Honda partnership will be potential winners next year, given it will be Honda's first engine, and every other team will be able to build on their 2014 cars and engines. Like Ferrari, McLaren have been struggling for a number of years now, and honestly I'd be surprised if Ferrari weren't the better option over the next two years.
But I guess he wants a change, McLaren will show him their strategy for success and Honda will bring the big bucks, but Red Bull, Williams and even Ferrari themselves currently seem like better options.
Maybe like Alonso's desire to win with Ferrari, he feels a win under the McLaren name (the team he always wanted to drive for) is just more attractive to him personally. But given his desire to win a 3rd title, surely performance is the way to go.