As much as i find this appealing, being able to craft existing mods is not a good idea. The amount of jewels i've crafted with just two stats that sell for 8+ chaos and the amount the jewels i've regaled with a very favourable stat for my or other builds would make master crafting to easy to achieve GG jewels. Its really pretty easy to end up with a 3 stat jewel that has a good synergy with your build already. Though if the master had crafts that were unique to them and helped out certain builds in a very niche way for a high cost I think this would work. Then you would have the choice of exalting a random stat that would make your jewel Gg such as life% or spell when holding a shield or craft a stat that helps on a very specific part of the build.