[Astarte]

>But it's disingenuous to claim that even using a private guard (which isn't possible, as far as I know)

I have been thinking about this for a while, too. There is some Tor fork which allows non-exit nodes to exit. It has been posted on tor-talk a while ago. For a private guard you would need to change the local consensus file and include the private guard. Then you would also need to control the next hop so it recognizes your guard as first hop and connect you to the third hop. I don't see why this won't work in principle.

[mirimir]

Huh. That is an interesting idea.

So you could have Tor exits that aren't published.

That would get around the CAPTCHA plague for Tor users.

Another option that I've considered is IPv6. Relays with both IPv4 and IPv6 must publish their IPv4, in order to get OKed for use. But as far as I know, there's no reason why they couldn't preferentially push exit traffic through IPv6. And indeed, use a different IPv6 address for each circuit.