This was originaly the site for those writing ages in the D'ni sense but there has allways been room for concept art and story writing. There are close links with the "Guild of Maintainers" GoMa
http://www.guildofmaintainers.org/index.php where they have a group of their own who also do age writing.
GoMa also do checking for cannon complience CYAN have made it clear that they hold cannon and have a right of veto over what is allowed and what is not (these are fairly loose rules) but the guys over at GoMa will cast an independent eye over your creativity a sort of neutral view. They will flag up anything that's not allowed baisicaly it's hands off Atrus and family and don't mess with ages they have allready created.
Any story can be in a D'ni age or world of your own creation. Living D'ni are probably not ok but conjecture about past events and historical figures as long as it's supposition and couched in doubt you should be ok.
It's like talking about the Pharoes in Eygpt you can can interpret the hyroglyphics but hard facts are thin on the ground.
The facts about various Kings are established cannon but you could create a story about an Age writer in the court of a particular King and the ages created for that King and provided they don't impact on current cannon then you are probably safe.
Specific questions can be directed at RAWA but don't expect a prompt reply.