FWIW, another (non-tlk) board I'm on changes a person's user title to read Banned (or "Banned Until" might be a tweak,) when they're banned.
I'm not saying it's an ideal solution for here, but it may be a simpler option to toss around than a notification list--on the one hand it avoids a public pillory (or notoriety) thread like a list could become, but at the same time, if someone is involved enough in a conversation that they notice they haven't gotten a reply when they're waiting on one, they can go back to the thread they were talking in and see under the poster's name that something changed about their status.
Because I sincerely doubt many people join a messageboard thinking they are going to be banned in order to fill a profile field out
(The only thing with the other board is that the word "Banned" is marked as censored for use by anyone other than Mods so members can't arbitrarily put it as their user title.)