Not my cup but his idea was about a mom who cuckolds her son, makes him clean her up after and maybe makes him clean her lovers up as well. Maybe moving on to making him service the lover beforehand as well.
Hey, if you wanna write it, write it. There's a niche here for everyone.
Yeah, most people won't enjoy a story featuring those elements - based on what I've seen, the mommy/son incest lovers tend to like a strong romantic relationship with the son being mom's only (except for male readers who often enjoy mom having some lesbian sex) - but there will be people who do enjoy it, and you should write for them and yourself.
I personally am always on the lookout for medium to hardcore incest rape, but there's not a lot of supply or demand for it, so I'm SOL ;op