Smithing. An obvious one to get raised, because of OSRS Items Dragon. Jagex suggested that Dragon Ore might be released. The QA where they were asked questions about the issue didn't give an exact answer, however they did mention that the protectors might not be happy. Although this was most likely an ode to Dragonkin, I'm straying off-topic. Dragon material is extremely rare at the moment. Why is that? It's not because it's weak. Currently I wear a rune. However I would like to have full Dragon.
Apart from certain weapons and the boots, it is rarely utilized in the game, simply because in the time it took Jagex to make it available to all players (and have they released everything? ) newer armor has been released, such as Barrows and we now have Bandos gear that doesn't degrade. The cost would be less when Dragon could be made smithable, which would make it more popular.
At first, I thought that this was enough. The entire range of Ranging armor fits nicely and we don't require any more D'hide gear. But then I realized I had not got Magic. In Dungeoneering and Stealing Creation, we can make use of Crafting to create Magic robes. In the present we are unable to craft Battlestaves. And Magic certainly could benefit from new armor.
To enhance the Combat Triangle, we need to improve our defense against melee. The only piece of Magic Armor that offers defense is the Arcane Spirit Shield. There are many others such as Ahrim's Robes Lunar Armor, Splitbark and Skeletal. But, they're all mediocre. While I understand that it is a basic Mage armor includes robes it is more than just the robes. It's magical robes.
It is possible for a mage to transform his robes to stop melee attacks. Bind spells can be used to stop a person from moving. It can also prevent the weapon from cutting. If Crafting was extended upwards, perhaps at higher level, you could create Mage robes to Buy RuneScape Gold enhance them using Runecrafting or magic.