There would be issues with having porn on Steemit. There isn't an identity verification process or even prompt asking if you're over 18 for Steemit. Yes, you're supposed to be over 13 to sign up, but even then, there's no restriction to the NSFW content already on Steemit. I think the way it's set up, Steemit could already be susceptible to lawsuits (at least in the USA) that they're supplying pornography to minors.
Having a mass-adoption of Steemit by the porn industry could be a boost to the value of the platform, but I think the clientele would change drastically. Rather than seeing people post about food, pictures, homesteading and crypto, you'd just see porn.
Personally, I think it makes more sense for some porn company to start their own blockchain-based site rather than take over here. They'd have more control and more of the profits.