In the same way that the current bboard allows the admin to choose one of three different styles
Various policies of how it looks should be separated from the underlying data model. I built a pretty deluxe blog module on top of bboard to find that because of the hardcoding of the three styles into PG and Oracle, it is basically impossible for an existing style to use the blog bboard without stripping various constraints from the PG model. PG w/o constraints? Yeah, that's almost down to MySQL.
A new bboard can be made much better, and that's been touched on many times before. So why not again. Unification with mailman or ezmlm, and either ubb support or some such stuff so that we neither have to slip into html just to quote something, nor are we open to javascript, other malicious HTML attacks, or just the whole unnested tag thing.