Rather than this being Paizo's response to 5e, I'd see it as a lead-up to a potential Pathfinder 2e.
Traditionally, D&D editions come out with the "let's throw drastically game-changing variants at the playerbase and see what sticks" books (1e Unearthed Arcana, 2e Player Options, 3e ToM/ToB/MoI, 4e Essentials) shortly before announcing a new edition, to allow them to effectively do a covert playtest of new-edition mechanics or recycle rejected versions of new-edition mechanics. There are only so many Advanced X and Ultimate Y books you can publish, after all, so now would be a good time to figure out if the players are as dead-set against ever having a new PF edition as they were when it first came out.