I through Brandon's response was very good, but the point which interested me most was actually something of a side note. He says right near the beginning:
It's worth noting in most of these discussions that, just as original sin is formally lack of original justice and materially concupiscence (craving for lesser goods) arising from such a lack, so hell is formally lack of contrition and materially penalty intrinsic or appropriate to such a lack. Everything else is either fully or partly symbolic, and no serious universalism is possible unless it accounts for universal contrition. (Most universalists don't even make an attempt at such an account, but a few -- like George MacDonald or Hans Urs von Balthasar -- do.)It strikes me that most claims that all must be saved center either around the idea that no one really sins all that seriously, or that God would be cruel to send anyone to hell even if they weren't contrite for their sins. Perhaps this is in part because people tend to have difficulty conceiving of hell as simply being the state of being eternally unrepentant (and the suffering being that which that would naturally imply.) Brandon's observation that any account of universalism must somehow include and account of universal contrition strikes me as very much on point. Obviously, one once gets to universal contrition, universal salvation is no problem at all. My own severe doubt that all could be saves is simply a doubt that all would be contrite.