Clearly it is a really good suggestion, just wondering why it hasn't implemented yet here.
Maybe you know, on the sister server, on Insania this feature is available, and let me allow to show its prize:
Here in Infinity a +0+0 FO Dragon Knight Armor costs 1595 credits, same item with +13+28 costs 1795 credits, compared to Insania same items cost 1200 and 3200 credits. If you still want harmony option to the item, it will cost more 1500 credits.
As you can see there is big difference between the +0 and +13 items on the two servers, so in my eyes if this feature will be implemented here, its price should be 1500 credits even more.