Just playing devils advocate here, and I could be wrong, but the Blomkamp concept art was very early days. It never even had a full script, only a 10 page treatment.
When you take into consideration Covenant's early concept art work and the fact it bares almost zero similarity to the final product, I wonder how much what we have seen would have been in Alien 5 anyway.
I always wanted Blomkamp to do an alien film after I saw Elysium, which I really like and was hyped when I heard he was doing it. Then I found out about him bringing back ripley, hicks and newt and I mentally checked out.
All hail Alien 3.