You see that is the beauty of a Grand Explorations book...you could keep all the OTU trimmings and set it somewhere completely different.
If the Ancients are the ones who carved up Jump Space into navigability corridors - Jump 1-6. Later they build expressways to allow them to move entire planets through jump space then entire systems through portals (ie Jump Gates just not physical ones like B5 but fields) but over time these would corrode and breakdown without regular repair work. Whilst, the younger races could skip along using M1-6 those superhighways could have exit points anywhere in Chartered Space and beyond (perhaps, it is the same route that the Primoridals use to the galactic centre).
Now, a freak experiment in 1116 learnt how to open and map a partial network of these hyper-spacial expressways but it was a classified military secret. Needless to say, attempts were made before. Some of these are the Lost Expeditions which would be the subject of Grand Explorations. You could throw Hivers to cooperate with Imperials, Solomani and Zhodani in this lost expanse as they search for a way home in another part of the galaxy or even neighboring galaxy (Magellanic Clouds or Andromeda) against the K'kree Steplords and their Aslan & Vargr underlings - who despite being meat eaters have their uses. Hence you could populate it with tons of alien races and lost human civilizations and maybe even victims of misjumps are not destroyed but end up here.
This has been a concept in MTU for some time. I once wanted to run entire campaign on this premise in the aftermath of the Solomani Rim War. For my location of the hyper-spacial expressways was in the Dark Nebula sector. In my own campaigns, the military secret was all but lost when Lucan purged the Grand Admirality but in a last act they hardwired the maps onto the latest warships. Most were destroyed in the line against Dulinor or Margaret or Solomani or Craig...etc. Some survived and made their way to Stephon who made their way to Norris. Some fell prey to the Black Imperium and Virus. That would be a subject of my 1248 Campaign...
