>>12308817I don't know. It seems pretty "essential" to the overall flow of the anime that there were at least two large "filler" arcs prior to the Gen 6 based anime beginning and the Plasma arc the started after the end of the Unova League seems to fit that bill very specifically well.
I'd be surprised if SOMEONE within the animation studio wasn't aware that Black2/White2 were coming, especially given that the Black/White game team had to have at least been somewhat aware sequels were in the works at the time the Black/White anime was being developed.
I think this is how they planned it
Rocket Vs. Plasma - Plasma introduced/ Rocket and Plasma are mutually defeated by Ash & friends, Ghetsis appears briefly via hologram, N is vaugely alluded to, Plasma appears to retreat forever, not to be mentioned until...
Episode N - basically planned as a post league "oh shit, Plasma wasn't dead after all!" in which they appear in the context of B/W2 plot to waste time till X&Y
