2 things I'd want to see:
1. An expansive marketplace for exclusive art and figurines. It'd be super cool if sculptors and artists could make con exclusive works for people to purchase and trade.

2. Artist panels. I don't think I've ever seen any convention spaces dedicated to pornographic artwork or the people who create it. Even at traditional cons, artists who draw porn usually dance around the subject or don't mention it at all so there could finally be a con where people could remark on their more adult art.

Honestly, if this was a thing, I'd attend it every time I could. Hopefully someone out there is reading this thread and planning to make it a reality.

this would be the con that would have the return of the yaoi pads and random orgies.

I mean you wouldn't need sanctioned fuck rooms. Isn't that what the hotel rooms are for?
Though if you do a midnight rave like so many anime conventions, that might turn into a messy orgy.

I see lots of people arguing about either it's legal or not. Some of you has raised questions about prices and paper works. But what I'm sure of is that even in US, not just here, in russia, there are actual places that will allow you to attend the thing with secrecy and less paper work.

Easy as it is, you just hire an underground or any other place that's just not getting into sight so easily, place an advertisement somewhere on site and you're off.

Such way, however, will make the place look like actually sexualy impacted. In a way that it would be slightly more lewd then it's gonna get. Underground place probably can be dark, so expect sex in open sight. Actual orgies could be arranged either, since you'll be in a secret place where all your "deep dark phantasies" come alive. And pretty much there will be hella big lewd dirty mess to clean up, and it may last for quite a while.

But I cannot see the lack of potential. R34-con is more then just an idea, it's probably great way to create a safe space where people could open themselves in lewd ways or just talk about sex and stuff. Our world, especially russia, is running low on such places, where people can just act out of bounds.
If I had money - I'd arrange it here, in russia.