I'm still hopeful that Covenant will get a sequel. It will most likely be the last one, and the one that ties into the original Alien. A lot of people have made a lot of good points on this site since the movie came out. The powers that be just have to find that sweet spot between Prometheus and the Xeno.
Prometheus came out and a lot of people were disappointed that the Xeno was nowhere to be found. Then the pendulum was moved across the spectrum to the point of Covenant being basically a full blown Alien movie. They need to find that sweet spot, in my opinion, of balancing the philosophical aspects of Prometheus and the Xeno of Alien.
I think the prequels tied their hands behind their back because of the nature of the Xeno. It bleeds acid. So you can't shoot it or blow it up if it's on your ship. So the only option is the airlock like in Alien and Aliens, which has obviously already been done.
The future of this series will be in whatever will hopefully be in Alien 5, and I'm not talking about the cancelled Alien 3.5. I'm also not talking about Ripley necessarily. If they have a great story to finish her out, then great. I don't believe the Engineers are done after Covenant. They can re-appear in an Alien 5 on other worlds. There can be different, exotic, and more deadlier versions of the Xeno. They need to do an Alien 5 in order to move away from the traditional Xeno that we have seen so far. Allowing the beast to change will allow the freedom to start giving us things we've never seen. That way you don't know what's going to happen already. Gives us a Xeno that can be shot or blown up on a ship because it wouldn't destroy the ship with the acid blood. To counter that perceived weakness, give it a higher intelligence so the hunt would have more tension. The scene that pops into my head is from Aliens when Hudson says, "How could they cut the power." I think that's why I liked the Neomorph in Covenant, and would have loved to see more of it. That little bastard was fast, lol.
I think if Alien is to survive as a franchise, and I agree with what some have said, it can't be a traditional space horror with stupid characters just there to be lambs to the slaughter. Alien 5 and beyond needs to keep the philosophical creation elements, I feel. It doesn't need to be front and center, but those elements will keep the audience engaged and thinking.