I also just tweeted Mearls about this, saying that I hope WotC embraces the OGL. He favorited my tweet.
I speculate that Mearls is an OGL supporter, and either a) they've already decided to do OGL, and Mearls wants to raise buzz, or b) they haven't decided whether or not to do OGL, and Mearls wants to convince the higher-ups that it's what the customers want.
Considering how much work Mearls got in the 3e/3.5 era under the d20 & OGL licenses, he'd have to be a bit of a hypocrite not to be an OGL fan. Mr. Mearls doesn't strike me as a hypocrite.
I could be wrong, however. I've been a pretty big fan of Schwalbs' work in the past but I thought his recent blog was 90+% full of crap.
I'd bet that there is a plan for a license & Mearls is pushing for the OGL to be used instead of the planned-for version.