What I'd like to see is the ability to get a personal identity SSL cert with tooling (browser plugins, for example) to make it easy to use on signup pages. This personal cert could have several fields, depending on how much information the user revealed to the certificate authority.
The primary field would be how much they paid for the certificate. That way people can be as anonymous as they want, and can get new IDs if they need, but they have to pay for each one. Then forums could require new users to have a certificate that cost at least a minimum amount, whatever is required to keep trolls away (that is, trolls who constantly sign up with new IDs). I'm thinking that $5.00 should be enough for most purposes. (There would be a minimal cost to cover the CA's expenses, however anything above that can be specified by the user depending on if they want a bronze level or platinum level certificate)
There could be additional fields that the CA verified, such as name, address, etc. These could also be marked as "Supplied to / verified by CA", but not included in the cert (so only the CA knows that info, and can have a policy of destroying their records shortly after verification). Or if needed (such as for financial transactions), name and address could be part of the cert.
The whole idea here is that forums could better control when troll users register multiple accounts -- yes, with the "completely anonymous" version of the cert the troll could keep buying new ones, but that is still a higher bar they have to cross than they do now.