Something that a lot of people seem to keep overlooking is that Covenant isn't the final Alien prequel apparently coming and it would make little sense for Alien 5 to come out before the entire prequel series is complete.
Is Prometheus actually part of the Alien prequel trilogy? Yes it is a prequel to Alien, but is it part of the trilogy leading into Alien? If so, that means we have at least one more movie after Covenant, if not then we may have two.
How many years away does that place Alienkamp? Add to that time any projects that Weaver, Bien and Blomkamp may start in the interim... I don't see it happening.
We will get an Alien 5, I just doubt it will follow its' current trajectory and will be at least half a decade away, maybe even a full decade away at fairly pessimistic.