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.
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That depends on what will happen during the Exotic Mission. It is unlikely, but one theory I've come across is that Maya might succeed in reactivating SIVA during the events of the mission, and the Plaguelands location is once again infested with SIVA. I'd be lying if I said it didn't have appeal, and it might add new meaning to the names of the various bosses in Reclaim if they somehow update the enemies to be infected with SIVA. Again, it is unlikely, given the amount of work that would be required to create SIVA variants for Maya's Cabal and Vex. I'd be pleasantly surprised if it happened, but unlikely. The Axe could be a means of taming some SIVA tech by combining it with Quicksilver nanites.