Ridley isn't restricting his or anybody elses future vision for this series, btw. Even if this planet is what we think, so what? This race have seeded the universe, deliberately. And we are worried by what appears to be the plot of this movie tying the hands of future movies? It's one planet, no matter if it's historically significant.
If Ridley decides he wants another planet to be full of engineers just down the road in the future, he will do just that. Similarly, any future directors could do it no problem at all.