Honestly, even if staying in the limits clearly set by Zorlun independently from Patreon (i.e. Katherine would never go to some extremes), the Katherine+Myriam has been something that has been coming as request already from long ago.
Unfortunately, Patreon's intervention has greatly complicated both the possibility of it happening, and what will effectively be in the game from this point of view.
Zorlun had originally said he had foreseen something, but Patreon basically forbade him from having Myriam and Katherine being in the same room while both having sexual activities, even if they are not having sexual activities between themselves - the definition of "incest" used by Patreon is their own.
There have been various ideas tossed to try somehow getting in part around it, but it is still unclear if and what will really happen in relation to that. But there is a lot of other opportunities for our Myriam to be "active"
.
By the way, since some asked in the past, the block of Patreon applies also to half-, step- etc., and anyway if I remember well Zorlun had never foreseen any "activity" between Marc and Katherine to happen, even before Patreon intervention, so much that
he used that kind of reference as a "trigger" for negative reaction by Myriam , so, even if you consider the version were he made Myriam and Anthony not married and having kids from previous relations, so Marc and Katherine as not being brother and sister, that is never going to happen.