I find it amusing how so many people here think that Blomkamp is being a selfish, narrow-minded elitist for opting to ignore Alien 3 and Alien: Resurrection with his new film. I've said it before and I'll say it again: He's actually coming from a far more common headspace of Alien fans here. It's far, far less common for people to like the third and fourth films than I think some members of this community realize.
Moreover, I don't think that anyone can just write off another person's credibility as a "fan" by basing it on whether or not they just like the first two films in the series. My dad and I totally disagree on Alien 3, but he's a huge fan of the series and has been since the release of the original film. I don't write off his opinion or love for the series just because his favorite entry is Aliens. Hell, the reason he's so adamant about his negative opinions on the latter films is directly because of his love for the first two entries.
The best option here, I think, is to just ignore A3 and A:R and continue the story from Aliens. Contrary to what certain dissenters of "rebooting/retconning" think, that actually does open up a lot more routes for creative stories than it would to just follow A:R. And before anyone asks, I'd be just as fine with ignoring Aliens and only following after Alien, but I'm rather positive that it's going to include Aliens in the canon of this new timeline.
I also don't think Blomkamp is going to 'sell out' and just retread Aliens. He's made it pretty clear that he's just as big a fan of the first film as he is the second, so I'm pretty confident that will play into what he comes up with. Especially since that one concept art seems to be indicating a return to the original "body horror" approach to the xenomorph's life cycle that was shown in the director's cut of Alien, while also including the Queen.