I don't think they changed the core concept. They've already updated his bio on the website and it still mentions Mizora and the pact, so he should still be a warlock. The new thing is that Mizora asks him to hunt down her enemies, including "devilish creatures".
Which I guess gives him good reason to turn against the grove, to take out all the devilish tieflings.
Or he decides to spare the tieflings.
At least, that's what I'm guessing.
But I'd love to hear from anyone who knows something about this? Hoping Wolfheart or someone will put out some information on what Wyll's like now.