That wasn't on Blomkamp either, that was on Fox. He wasn't pushing for the film; he posted some fan art, fans lost their shit, the noise got Fox's ear, they started toying with developing the concept.
He made a formal pitch in a meeting with Fox. The art he posted online was from that pitch. Although he said that "Fox never said no" he didn't think that he was going to do it anymore. Which is why he posted the pitch art online, same thing with all the Halo stuff he made. It's quite common, happens with lots of abandoned film proposals.
So he was obviously pushing for the film at one stage but by the time he posted the pitch art online he wasn't really interested anymore.
Not sure why certain nutters on here are getting their knickers in a knot over Blomkamp wanting to make an Alien film while Prometheus II wasn't even in active pre-production. Prometheus II's production only resumed in earnest after Blomkamp's pitch and for a while the two films were being developed concurrently for a 2017 release for both. But at one point Fox likely decided to play it safe and only develop one film for now and so decided to pursue the Prometheus sequel but now with added Aliens and 90% less Prometheusy stuff.