[quote=@Yahrlan]
Would a tab in the RP thread (like the IC/OOC/Characters tabs) be a viable compromise? Could be 'References' tab? Can be used for world-building, linking to other RPs in the same "series" or world, linking to outside references etc without needing a new sub forum/section. 
[/quote]

Like Poi said, just use the OOC. Or like ArenaSnow previously said, just make a wiki or something. There's no need to add any tabs or subforums or anything.