It doesn't sound like they decided together. I first heard a rumour of Nikita & Viktoria trying out back in January but I thought it was ridiculous & ignored it, and since then Elena has been talking about plans for shows after worlds, making a new exhibition, how they both wanted to bring back 2 gold medals from the Olympics in 2018. And then when the report in ITAR-TASS appeared Elena was talking to some girls on I/K's vk fan page and when they asked her about it she said "I have no idea about this, Nikita and Morozov have said nothing, how could anyone expect me to skate this week if it is true." Sounds like it was all fixed up behind her back.
I don't really see either partnership working - Elena will overshadow Ruslan on the ice personality-wise, and Nikita already struggled lifting Elena and he's had back problems as long as they've been senior, Viktoria is bigger and taller so I can't see that getting better. Plus she'll probably have Morozov creeping all over her.