The reason the Mihon de said that is because j2k is using an older tachiyomi base iirc. Updates on it have been on the slower side.
It's still being actively worked though (as far as I know) and it still works fine, so there's no reason to switch off of it for now. If Jay does drop it then you should move onto mihon or its forks (TachiyomoSY and TachiyomiAZ will be based off of mihon in future versions).
It's not really Twitch's fault. Twitch doesn't care about sexual content, they're a company they don't have morals. They'd be more than happy to rake in those dollars. The problem are advertisers and payment processors who have very strict views/policies on stuff like this and Twitch has to kowtow to them if they want to be in business.
So many sites have this happen to them, where they allow or even encourage sexual expression and then a payment processor comes in and says "yeah if you don't cut out that we're dropping you" and then it's over.