I'd bet that this is all about the Triple Crown. I'd look next for an announcement about him going Indy cars ... and probably a seat in whatever Prototype team looks dominant.
Quote from Motorsport.com article:
McLaren said he was not allowed to repeat his Indy bid this season, but did give Alonso permission to combine his F1 efforts with a full FIA World Endurance Championship superseason campaign.
Alonso went on to win the Le Mans 24 Hours at the first attempt with Toyota.
With two Monaco GP wins under his belt, Alonso's Le Mans victory leaves just Indy unconquered in his bid for motorsport's unofficial 'triple crown'.
Alonso is extremely unlikely to add to his tally of 32 grand prix victories before he leaves F1 at the end of the year, and is just three shy of hitting 100 podiums. end Quote.
BTW, Alonso and Toyota did something that really earned my respect at LeMans. In the waning hours of practice, Alonso/Toyota was the last team on the track practicing (hard!!!) ... and stayed there until the session was officially ended. Everybody else had quit practice many laps before.
I don't think this extra practice made them any faster ... clearly Toyota was the class of the field. But there they were, still pounding out practice laps. Surely this extra effort impressed the other team members that Toyota and Alonso were there to WIN!