i think it's entirely possible but (gestures to the newly announced stream) i think it's looking pretty unlikely now.

rui tanabe has a perfect track record for announcing mafuyu events. it seems she's pretty easily accessible for this.
satohina more often than not appears for when mizuki events are announced. she's appeared 4/6 times. the two times she missed it were kimi no yoru wo kure, and bake no hana. bake no hana was on anniversary stream, too. so missing it kinda.. makes some sense
story setup leaves plenty of room for them to have mafuyu event next. it's very likely she is in fact coming up with a new event, so i wouldn't bet on anything otherwise

in which case, with a mafuyu event being announced it does lower her bfes chances like, majorly
-if niigo event is announced FIRST as mafuyu there is still a chance it's her
-if niigo event is announced SECOND as mafuyu THERE IS NO CHANCE
-if niigo event is announced as mizuki, uh. maybe???

i think the second outcome is the most likely due to mmj's current weird situation with shizuai lims and gaps and events lol.