I've thought of that possible outcome, I just think it would be an easier sell to Asami if Shizuka can get in on the happiness MC does rather than try to convince her it's fine to also enjoy her daughters partner.I think it might be like what you said but the other way around, I think we'll have sex with Shizuka first and get caught by her mom. Shizuka has already asked to have sex with us, and she not only knows about all the incest going on and is ok with iit but she's supportive of our getting with Nana.
So I'd say we get caught getting sexual with Shizuka and she invites her mom to join, being very convincing. She'll probably name drop Cat and Liz as being a mother daughter duo who are sleeping with us together and are our aunt/cousin.
I do admit it can play out your way just as much as I view it however, I just hope we get them both together in bed.
I'm ultimately just waiting to see what MB has in store for us, I personally have enjoyed at least 80% of what happens and only indifferent to the rest with the exception of the cuck content with the couple. (Not saying it should be removed, but just not for me)