At this point (being unofficial) we are not making ages for MO;UL, so it is not outside of our scope to do ages based on the D'ni.
When (if?) Cyan accepts us as the official Guild of Writers, they may lay down some ground rules about what we can and can not create.
My opinion is that we will be able to make D'ni based ages, but they will be much much harder to get accepted for MO;UL. You are right that ages of completely original design will most likely be preferred, but I would not stifle anyones creativity until we have to cross that bridge.