Although the design has not yet been completed (it's about half-way there) what I have envisioned doing with regards to accounts is to have a regular need to provide a difficult (and memory exhaustive) POW so that you can't create Sybils without incurring more and more POW.

This also means that new accounts can only be created at this same time which you could think of as being like a regular "meeting" of all those wanting to continue to mint blocks (if you fail to provide POW at this time then you'd lose the right to mint until the next such meeting is held).

Note that these meetings are not like a real meeting but perhaps are just txs that need to be included using information only revealed after block X that must be included with the POW in block X+n (where at a minimum n would be 1 but more like >10 as the POW would be difficult).

Most likely the system will also support accounts that don't get to mint at all (so they don't have to provide the difficult POW although they might be required to provide at least some POW to minimise that as a potential attack vector).