I pointed this out in another thread but gonna say it again here: Its very easy to make YoRHa fit into XIV without making it involve anything outside the planet (other then Omega jumpstarting Allagan tech)
In the Fractal dungeon we encounter Manikans, which look like Hyurs (if they weren't once Hyurs/clones given that they are found in Fractal). They are a nod to the Manikins of Dissidia.
The Manikins are revealed in 012 to have been created from materials found in the Void, being able to grow into copies of those around them but having no will of their own essentially being puppets. Chaos, Cosmos, and even the Dissidia version of 1's Warrior of Light are revealed to be Manikins, with a few other characters theorizing that they might also be such.
In NieR: Automata its eventually revealed that the YoRHa androids have the same core as the Machines they fight, making a very similar case there to that of the Machines, that alongside how human-like the machines have become they are more alike then anyone thought outside those who were in the know.
Point being outside the spoilers, YoRHa could easily be varients of the Manikins, either as an elite version of them or a varient that survived to the present day. If anything it isn't the YoRHa you should be worried about being in XIV, its what else in NieR and more importantly, Drakengard, might be brought into the game as well.