So many roadblocks. We have Avatar 2, 3, and 4 to worry about but scenes for those movies are being shot out of order and in a haphazard fashion, Cameron described it as a sort of jigsaw puzzle. Not too worried about them.
But then we haven't had a The Gone World update yet. And then we still have two more Alien prequels. But Scott will surely film something in between Covenant and the next prequel. So when the final prequel comes out in 2021(two year gap seems reasonable), Alien 5 could come out in 2023!