I'll be interested to see how much of Earendel's stuff makes it into the DLC. They hired him as a concept artist officially - which makes sense given his beautiful work on Alien Biomes - but they have also talked a lot in the past about expanding Factorio into space, and his Space Exploration seems like a decent intellectual property pick-up for them if he did in fact turn it over.
I'm waiting to see some official info. I had a go at SE and RSO when it was released but it got a bit complex - par tof work in RSO is actually done. There is still the most tricky part - how to do some special stuff that SE does on various areas and how to balance RSO on finite areas with varied configs.
A lot will depend on the what if's about dlc being some variant of SE or not :D