I'm thinking about the formats a board can take. Quite a palette can be observed on Endchan itself.
Probably the first thing that would come to mind if the board is:
I. anything goes (NSFW content can be restricted) /b/ type;
II. themed.

Then the next division could be the:
A. single active thread;
B. many active threads;
...formats.

The single active thread format, can be divided further:
A/1. preservative/archiving - where previous, now autosaging threads are left open (or sometimes locked), preserved, archived;
A/2. forgetful - where previous threads are deleted.
These sets could be applied to the many active thread format, but it kinda lose it's meaning as new threads will more quickly kill older threads than how the A/1 case does. Unless there is no page limit.

Then threads themselves can be themed or not:
a. arbitrary - when threads are opened on the users' whim
b. generals - when posts belonging to the same topic/theme are collected into specific threads.
I do not consider these type of sets which would make a basic divisions between boards, since these can be applied in a mix on one board.

At this point this is a very rough concept, just some observations thrown on each other. Tried to give it a structure but not a matured construct.
What Bernd thinks? What would he change, add, remove, redraw?