Here's the story. I had been hoping for Sylvie Goulard, a woman and a centrist, but Philippe makes more political sense for a president who must put together a majority with elements of the center-right as well as the center-left. The nomination is Juppé's revenge. It is also Michel Rocard's revenge, since Philippe was apparently a Rocardian in his youth.
Of course, this odd convergence in the center, so at odds with French tradition, will put both extremes on the new government even before it is formed. Macron is banking on a German-style Grand Coalition. What emerges from this will of course depend on the balance of power determined by the legislative elections. Until then we commentators will be speculating in a void.
ADDENDUM: The new PM profiles ... Mélenchon.