It would fall under bestiality not gay as Cassius is a dog and just because a tag isn't there now doesn't mean it can't appear later on in a game as tags at the top can only be there if they're in the game.
Sorry, my mistake. I was thinking in terms of male-male, but you are right that I think the term "bestiality" can be used for any kind of sexual interaction with animals (though quite actually, it is not the only possible use of the term "bestiality", just the one we use in the forum, given the subject of the forum and the games
).
About the addition, I doubt it - Zorlun has never indicated any plan whatsoever to add that to the game, and although he is trying to satisfy as many "customers" as possible, he is also a bit using his interests, and that is not part of them.
For me there is no link between Myriam and Marc. For me I just don't like them.
Uh, if you don't like the main character of the game, I am not sure how much appeal the game can really have for you, but you know better what is the appeal of the game for you.
About the "no link between Myriam and Marc", honestly, I know the "for me" indicates an opinion, and I myself expressed some personal opinions, but...
If you play with the incest, they are mother and son.
If you are playing the "Patreon no incest" version (I think you are using the "Prometheus" version, not the Patreon version, since you mention Cassius), even if you are making sure she never does "anything" with Marc, then, Marc is the son of her partner (at the start) Anthony, and she feels he his like a son to her (she is that kind of maternal, protective person), so, she feel a connection to him anyway .
So, the link between them is a part of the game that is there by definition from the start, and cannot be eliminated - even if Zorlun killed Marc, the link between them was there in the game up to 3.03b, so, would still be there.