Small suggestion....
I've lately had a lot of ideas for books I'd like to write for my current PC but it would be not entirely appropriate to have them readily available on the forums. A forum for writing books of a more forbidden nature that have no other place they would appear logically or would not be suitable to the forums would be useful. It feels a bit clumsy writing them into your PCN. Having one PCN-like forum dedicated to this would make DMs looking for neat books of a hidden nature to turn into IG books or placeables of some variety, far easier as an added side benefit.
I had this same idea, a hidden IC type forum (for books or research that might be spoilers).
As far as I'm aware, this sort of forum does, in fact, already exist. Though being granted default access and only being viewable by the authors of each topic and the DM team would be a big plus!
2manyforumsasitstands.
Post books in your PCN notes. Dms will add as they think appropriate.
Of course, if dms want this sort of forum, more power to them, but I recall Dms mentioning that they already have loads of forum work to do. :(