I'm pretty sure this is referencing the moment from Roselia's live in which they were performing ONENESS and Aiba-san (Yukina's seiyuu) does exactly that to KodouHaru-san (Sayo's seiyuu). And how Aiba-san is just smiling through it all is absolutely adorable!!
In general I love seeing Touhou characters in alt modern clothes but this one Reimu's design is cool and refreshing while Yukari's design is so amazingly good.
Compared to the two other Madoka Magica crack ships (imo), Sayaka x Homura, Kyouko x Homura, this one is probably the most far fetched one. Maybe it's because of Maitake but I can see the Homura ones maybe working out, I haven't seen anything for this ship lol.