Given that most of the off-topic discussions that happen here worth continuing are born between a small group of people arguing, I don’t see the problem with that. Just say you’ll take the discussion to a PM and that you’ll invite people who are interested. Removes clutter for the people that don’t care and allows those who do to continue their discussion.
Er, no? I can’t feel it. It’s still behind the massive anonymous wall of the internet and it’s just a small discussion. Not to mention that if you’re continuing a topic (which is what we’re talking about here) then you already have something to work off of so there’s not really any reason for getting locked up and being unable to write things. The only thing that’d make it awkward is if you approach it with a negative mindset.
Also, you know where else you may have intimate, one-on-one discussions? With your friends, with your family, and with people you just like or know in general. I’m pretty sure making eye contact when having a discussion is pretty common, and you can’t say that you’ve never had relaxed discussions or debates with people. Nothing wrong with getting to know somebody a bit better, even if it’s through debate.
Not sure why you highlighted Kazamatsuri and Key there, but generally if there’s really enough community interest around a topic people will express that. As I said above, most of these discussions are born from a few people arguing, and can that really be called a community interest?
Regardless of all this, no, we’re not getting an off-topic discussion. And that’s pretty much that.