I have decided that I'll develop Dark Nebula for Classic Traveller. The main reason for this is that Dark Nebula, at its core, is a Traveller setting. And Classic Traveller is a great, and very freeform, ruleset. HOWEVER, I also intend to insert bits and pieces of Stars Without Number into it, namely world tags (factions would be more difficult to convert as they use the SWN OD&D-inspired mechanics). World tags, after all, are system-neutral, and so are the various plot hooks arising from them. I'll fit them, however, to the already-existing Traveller UWPs and trade classifications of this area of space.
So Traveller it is for Dark Nebula!