I think Dan is wrong here: he should lay out what he want to the other Dom ahead of time. What is the worst that will happen? the other Dom isn't into it. At least you can decide if it is worth it. To say, I don't see the harm in waiting, Dan is LAME, IMHO.

1, there is a 100% chance that many people are down with this.

Get on fetlife. Figure out how to network. Go slooooooow.

If I understand Dan's advice here, it is spring this scene on your sub's other Dom once the scene is in progress. That doesn't strike me as a good idea; scene details should be worked out in advance to avoid miscommunication, in-scene issues, and post-scene issues.

As for whether your sub's other Dom is likely to be into this scene, they already can have their way with your/their sub in their own scene. So I'm not sure what's in it for them (even if they have switch tendencies).

Top.
Middle.
Bottom.

This is nothing new.

The complete fantasy: "I tie my sub to . . . various other highly specific things. . . (and I get Dan to publish it)."

If it isn't Dom Perignon, IDGAF

Honestly, as a Dom, I would totally hate this idea.

For me, I get the fantasy of control in the space with my partner(s). This would, literally, do nothing but smash in my face that I am not the one in control and the other partner is.

I'm not perceiving any existing friendship or relationship between the OP and #2 so I wonder if this is some kind of power play. Given that so much of kinky power play is about perception, I see it as super risky to the dynamic between the sub and the second partner. I would go so far as to say that it would probably compromise their relationship.

So, sure, it might work but that's going to depend on #2 and their willingness to engage in the scenario.

I don't remember this one.

What an extraordinarily bad idea.
This might work with a dom who was friends with #1, but did not play regularly with the sub, however not with a the sub's other dom. This could ruin #2's relationship with the sub. Exactly what's in it for #2? Doesn't he get to play with the sub regularly without being subject to interruption? Perhaps offering to do the reverse at his place some other time might help.

Is this something I should talk with the other Dom about beforehand . . .
Are you kidding me?
Communication is necessary for consent. But as Dan said, scheduling.

Switches exist. It's completely possible to dom Person A and sub to Person B.

What does the other Dom get out of it? He gets to satisfy his sub, she's into it. He must be asked ahead of it though, consent as @8 vab251 mentioned, and being a Dom, he can't afford to lose that edge because he's been taken by surprise.
I agree with MonkeyFetish @7, sounds like some sort of power play, and the LW should read the Dom rule book again.

Nyckname @4: Except that in the BDSM world they're called "Dom, switch, sub."

"Is this something I should talk with the other Dom about beforehand or should I just do it and see what happens?" No matter what in the realm of BDSM "it" is, the answer is ALWAYS to talk about it beforehand! In this particular situation, I can't see how the surprise element would lead to anything but hurt feelings and disappointment. What, DOM asks another dude to dominate his sub, then comes in mid-scene and demands that he stop and just leave? How rude is that? Of course the terms -- all of the terms -- of the scene must be laid out in advance.

One thing that wasn't clear is whether the other Dom is a hypothetical person. From the sentence "I've talked to my sub, and she is really into that scene, but she doesn't know how her other Dom would feel about it," it sounds like this third (a Domicorn?) does exist. If so, Sub should ask him how he feels about the scene, then the three of them should meet up to work out details.

"Is this something I should talk with the other Dom about beforehand or should I just do it and see what happens?"

Um, are you kidding me? The answer to this question is always, always going to be TALK TO THE OTHER PERSON BEFOREHAND! Seriously, you're unsure how the third person in your S&M scenario might respond, and concerned that they might not be ok with it, so you're wondering if you should ask them about it or just surprise them with it mid-scene? The fuck? How is this even a question? GET CONSENT!

Did Dan just recommend tying someone up, and then inviting whatever random person from snapchat and leaving the tied up person to fend for themselves?

@9, Yes, we switches exist. However, from what I've heard, it is unusual that a D/s pair will switch with each other. I certainly haven't done it. It is also uncommon that a switch will sub to a dom in the presence of the switch's sub. What is somewhat common are couples who are both doms and play with subs together where both doms cooperate. One of these may sub to the other, but most likely only one on one.

The D/s dynamic works well when power is exchanged and the parties take on a (or connect with an inner) persona. To keep this believable, revealing the opposite persona could be counterproductive.

A modification to the proposed scene that might make it work would be that #2 is guaranteed a certain amount of time, and #1 might arrive early, and then wait for the hand off.

Rare bad advice from Dan. Surprises during scenes sound hot and "spontaneous" but springing something on a scene (or sex) partner is a dangerous gambit. Many many ways it can go sideways.

I've topped another dom's bottom, with the other top right there watching and in some ways sub to me as I showed him how you "really" top a woman. If he had suddenly asked me to go in the middle, I'd probably interpret it as something having gone terribly wrong. Just communicate beforehand!

Yes, without question, talk to the other Dom first, & figure out if they're into it.
Perhaps they might even have some devious amendments or variations that could make the whole scene better. And if they aren't into it? Catastrophe avoided. I recommend taking the other Dom out for drinks with the expressed purpose to discuss such a scene.
Consent consent consent. Consent? Consent!

Now, since the sub in question already knows about & consents to this idea, springing it on her would be plenty fun. But don't do that to someone you expect to 'top' (in whatever format) but have not previously communicated with.

That said, TWO doms at the same time is a barrel of fun for everyone (in my humble experience), and gives each dom/me the opportunity to 'tag out' and take a break while the other one continues the play. Dom/me'ing is a lot of work, and many hands...

Another hot option: Sub gets topped by Dom A, then Dom B arrives and tops both of them (bcz Dom A is really a switch)... yum. That could make the sub feel extra subby, because s/he is now subbing to a sub, and is therefore even subbier than normal. Oh the debasement!

@11 Then why is "Middle" a role option on Fetlife?

@18/Nyckname: Big, Middle, and Little. That's an age play or Daddy(Mommy)/little type dynamic.

@19 "middle (or middles): 2. in multi-top scenes, an assistant top, literally between the senior top and the bottom(s); or a senior sub; or a 'switch' who subs to the top, and tops the sub." ~ https://fetlife.com/groups/3243/group_po…

Nyckname @20: The more you know. Language keeps evolving. I would have assumed "middle" would be defined as a person who wants most of the attention in a threesome. You're right, though -- an "assistant top" is different to a switch, which is someone who can either dom or sub, depending presumably on what role their partner takes.

Middle as a go between 'twixt a Top and a bottom has been around since at least as early as 1986, which, coincidentally, is when I got into the scene. Using it to describe adult children is somewhat more recent.

@15 -- One of the coolest scenes I ever participated in was with another switch, and we switched every couple of minutes during the same scene. I could feel the power like a live and tangible thing as we passed it back and forth between us. So extremely switchy switches do exist. :-)

@23,
Very cool, but how common do you think this is?

@24 -- I think it's more possible than most people realize, because BDSM community norms tend to enforce staying in role; that's why I'm going to the trouble of reminding folks that other things exist.

@25 I'm assuming you're not both into heavy bondage. Kind'f hard to swap off roles mid-scene with that.

While I've heard of others going back and forth in the same session, I bet it's more common to have some sort of contest in advance to determine either roles for the night or who does what first.

@15,23,24 - I can't speak to 'how common', since stats are somewhat hard to come by. But I've definitely switched mid scene, and I have partners with whom we trade D/s roles at different times... it's great fun!