Well you can always have a reserved post on OOC for uploading world building. , or the zeroth to allow co gm to edit. 

Also adding a new tab means most RP not use it likely? the only way might be to have a optimal tick box when setting one up to activate the extra world building page on creation. SO that if one needs it has the option, if not then it does not. 

This would have to be in creation as i doubt you can add once thread made, coding wise, saving info, sounds like a headache. 

but this would also require reworking all the notification, saved RP tabs, etc, and that im sure is probably something that might be a lot of work.