I wouldn't equate prostitution with porn production. Prostitution implies an exchange of money. Porn can be produced without money.

In the same work by Engels that you are referencing, he is writing about abolition of the family unit. He says that the family unit and monogamy exists because women are dependent on men under patriarchy and monogamy gives men power over women. Engels says that without patriarchy, children will be raised by the community rather than by individual families.

Our sexual love differs essentially from the simple sexual desire, the Eros, of the ancients. In the first place, it assumes that the person loved returns the love; to this extent the woman is on an equal footing with the man, whereas in the Eros of antiquity she was often not even asked. Secondly, our sexual love has a degree of intensity and duration which makes both lovers feel that non-possession and separation are a great, if not the greatest, calamity; to possess one another, they risk high stakes, even life itself. In the ancient world this happened only, if at all, in adultery. And, finally, there arises a new moral standard in the judgment of a sexual relationship. We do not only ask, was it within or outside marriage? But also, did it spring from love and reciprocated love or not? Of course, this new standard has fared no better in feudal or bourgeois practice than all the other standards of morality – it is ignored. But neither does it fare any worse. It is recognized just as much as they are – in theory, on paper. And for the present it cannot ask anything more.

Engels says that without the confines of monogamous marriage and the family unit, with women having equal footing in society, people are free to have sex for the purpose of love. I wouldn't say that people are limited to having sex for the purpose of love. It also doesn't mention filming the sex. It's also very heteronormative, but that is something else. The point of Engel's writing is that he's saying ending the family unit will give people, particularly women, more sexual freedom. It's not about enforcing heterosexuality or monogamy or limiting sex.

Editting my post to say that it's very weird that you think the word "cuckold" is related to porn. Engels used the word cuckold in the writing to describe an abusive husband whose wife decided to cheat on him. Not related to porn at all. Engels just sort of implies that adultery will be less likely in the future because women will have economic independence, leave men instead of cheating.