This topic is really dear to me as I'm a 43 year old guy that has never been able to find a hotwifing spouse that was very compatible with me. I did find a couple of FWB's that would have liked a marriage with me and swinging, but they were not compatible with me much aside from kinky stuff.
I was fit enough, etc.... to end up being a young buck for some hotwives in my 20's. I learned about polyamory at age 25, but I didn't tell the hotwife couples about poly. I told my FWBs. I had 2 FWBs that were interested in threesome and being able to have hookups on our own, but they did NOT like the idea of polyamory. They were women that vote conservatively, but just aren't sold on sexual monogamy. That's really common when it comes to casual sexy types of open relationships, but outside the realm of this topic, mostly.
So, I moved to a popular city by age 29 and started going to polyamory events. I ended up dating a married poly woman for 6 yrs +. I did get some cuckolding fulfillment out of that relationship because she did get off harder on bigger dildos, and one of her other guys was really well endowed too. I told her about cuckolding, and we started to frame it that way. He never let me watch until my birthday one year. So, that was very difficult to live with, and is NOT uncommon in polyamory.
Also, poly women are less likely to want to go bareback with lovers. There's some exceptions, but I've seen it in surveys and also in real life. Swinger types are much more likely to be into bareback sex, which is usually a major theme in cuckolding. Last, women that identify as poly might want to do things very separate without much input from you, or without telling you many details. So, it's a big gamble. Yes, you can be more certain of being with a woman that has sex with other men by going the poly route, but they might have sex with unimpressive guys and also not ever let you watch.
So, my advice is to try and date women that do not identify as polyamorous, unless she is a Domme that likes cuckolding too. You can post ads on kink sites and apps for that, but don't place the majority of your hope there. It's just prudent to put an add on those places, and focus on other non-kink sites.
Okcupid has a non-monogamous identifier label on ads. So, you can choose to see profiles of only non-monogamous women. Pay close attention. Most of them will be poly. A few of them will be the more casual "just open" types. Try your best to spot those.
I've used "monogamish" to describe myself on an Okcupid profile, and selected to only be matched with non-monogamous women. That did get me connected with women that were not monogamous, but most of them were closer to poly. Again...... It's a steep mountain to climb, getting cuckolding with poly types.
I'm going to use Okcupid again soon. I'll choose the non-monogamous identifier up near my height, etc... on the profile, but in the paragraphs about myself, the most I will say is "kink friendly". That's it. Also, Okcupid has many multiple choice matching questions. In there you can answer questions about open relationships, etc.....
Feeld is an app full of non-monogamous women. Only the best writers could probably do well mentioning cuckolding on their profile on Feeld. That would not include me. I'm going to probably mention that I like a mostly one-sided open relationship on there. Adultfriendfinder can be treated like Feeld, but know that there's many more males on there, and don't count on it as your big winner.
Regular vanilla dating apps...... use those. Go on dates and try and get better at dating. I don't have a great answer about when to mention an interest hotwifing, but I do think you are correct in mentioning MFM threesomes first. Then, the next thing to mention, if she is not into threesomes, is the advice given above that you would be fine being in a relationship where the woman had flings now and then if she wanted to. This topic comes up sooner for me because I admit my past in polyamory. For someone like you, it's not a first or second date topic. I don't know when, but not early!
I've been surprised lately by how many men have approached the subject of hotwifing by not using labels, but instead telling their partner that they could fool around if they wanted to. That makes a lot of sense to me because you are not asking them to take on a new label, but just telling them that a common taboo mistake that other people make, is actually OKAY with you. Asking a vanilla woman to be poly or a swinger is a big deal, as those are whole lifestyles that people have assumptions about, and many people do not want a new label for themselves.
I myself think that I've wasted time dating in the poly community when instead I should have been going on many dates with many different women, and not having sex early, but definitely having good conversations about sex when the topic comes up on it's own. I could have found a spouse that way by now, I'm fairly sure.
Basically, I didn't date around enough and I tried to take a short cut. The only thing I got was guaranteed non-monogamy.
