In this system you could still have throwaways, but the throwaway has to be invited/created from another account. This way you can create as many throwaways as needed but if you behave badly with your throwaway and it gets banned, then your main account is prevented from inviting new users and creating throwaways. Trolls could create new, primary, accounts but someone would still need to invite them back in. I definitely don't think that this would eliminate them, but it could potentially slow them down.

And because the moderators have the tree of invites it's pretty easy to determine which branches are yielding troll accounts and prune further up if necessary.