I'm A Banana
Potassium-Rich
With 5e doing so well it seems all well and good that other companies might want to join in and produce compatible content. But that gets tricky if, suddenly, WotC decides to produce an adventure that's too similar to something they planned, or changes the licence, or decides to release 6e. That's going to affect their company's sales and future.
I imagine [MENTION=1]Morrus[/MENTION] can give some interesting insight to what happens when an edition-change happens mid-Adventure Path. I'd wager it's not pretty.
While I don't imagine Paizo going whole-hog on 5e, I wouldn't be shocked if they had some support if there was a good, open license. From where I'm standing, Ryan Dancey has been proven pretty right about the OGL's benefit to WotC, it's only a question of if WotC realizes that and embraces the OGL (or something similar) or not.