I pretty much thought about this because The states of both worlds are pretty similar in terms of the cities and everything are in a decaying vine covered and rubble state, and it could be interesting due to the Robots, Beast Packs, Androids, as well as the Rouges in the middle (as well as the Waddle Dee Town in the middle of everything else).
so it'll either be two plots at once at the same time or it could be the duo heroes meeting up somewhere in the middle, but to be fair it would be somewhat difficult to put everything in the same thing, and I think 2B and 9S would have mixed opinions of Kirby, and the only 2 places where they could even team up would be at the Carnival Area (Wonderia Remains/Whatever the Automata one is, I forgot as wel as the Lab places) and they are also different both in actual Map placements (Only thing similar would be the Lab and the Desert, but that's it).
although you could kinda have them split up to do their own things, like for example, have the Kirby and Bandana Dee Duo go from the carnival place to the Ice place and the 2B go to the Castle place (There is no Ice place in the Nier Automata, and there is no actual castle area in Forgotten lands), but to be fair, you can do your best to shove the Forgotten Lands plot into Nier Automata like some of the other writers do (aka, like I just mentioned, shove the Forgotten Lands plot into the series it's crossing over into).
but in that case, why not have the four split up into different sections of the area instead, like maybe wonderia is just what the beast pack call the place and they get split up and fight their respective bosses and then they join back up at the Ice place?
I mean I know the part about the humans doesn't lineup, but either way they are gone anyways. I do not know if anyone did a crossover of the two yet. although a potential Scuffle/Battle between Meta Knight and A2 would be pretty neat.
