As has been stated above in less detail, the ONLY reason royal items were and are rising is because of the fact that they had just been released, and not many people have been able to loot the items. However, as more people create hunter pures to loot royal items, the Supply will meet the demand and the price shall drop and stabilize at a much lower price. This is what happened to the Rune Berserker Shield, but over a period of 6 weeks. It started at 70k, rose to 450k+, and dropped again to 150k.
As regards to merchanting them, when they are near rock bottom price, you can buy lots of them and profit from the inevitable bounce.