[e2le]

Perhaps a potential solution is POW based registration, registration is slow and CPU heavy. I don't think it's likely there is going to be a perfect solution to this and might be that it's better to slow down bad users and make it expensive to ban evade.

[ChainOfFools]

This will just end up promoting the interests of already wealthy bad actors, and fomenting user cartelification behind a screen of anonymity. See also: Bitcoin

[Zaak]

That's a very interesting idea, though it wouldn't significantly affect people with vast resources such as botnet owners, corporations, and governments. It would certainly slow down the garden-variety troll, however the determined troll would just keep a core burning to create a steady stream of sock puppet accounts.