This could be an opportunity to turn the plaguelands into a new "plague lands" but instead of destructive siva nanites infecting everything, and splicers running around everywhere, it could be an area where the newer version of nanites from the exotic axe could restore, build, and heal everything. The plaguelands could be this super lush green area with more vegetation. i could imagine these new nanites would also build off the scrap metal and rubble. turning it into somewhat of a paradise with defensive capabilities. So, if you want to give the cabal a reason to be in an old area, then that should be the reason. They want to use this version of nanites to make themselves stronger, being able to experiment with weapons that heal them etc. Imagine a new breed of cabal soldiers that have liquid metal arsenal like the T-1000. There's a potential plot in there to revamp an old area with a twist on a similar story, with a newer version of nanite tech, etc. Sure, its repeating a story, but it could be used to introduce new loot and gear as well as make the plague lands interesting.