If anything, I'm guessing it'll be like the MCMMO mod...
In that mod, you could use an iron block as an anvil. Once you place it, you could right click with any iron, gold, or diamond armor or tool and it would use one of the respective ingots/gems from your inventory to replenish some of the durability. Initially you didn't get much back per ingot (it was probably about the same as the cost of just making a new tool/armor), but the more you used it, the more efficient each repairing action got, until you could eventually fully repair a diamond breastplate for a diamond or two.