If blizz wanted to make the blacksmiths able to repair armors of plate and mail, they should consider creating some patch kits of metals and mail that can be mined or purchased. 

To work well with other professions and promote a better economy, the bs kits should require something like adamantite or fel iron ore and some fel iron or adamantite bolts from and engineer.  A portable forge requiring wood and flint and or a couple of motes of fire would prolly work well to be able to repair during a raid rather than to hearth and resummon back.

Tailors should be able to reapir cloth items with cloth armor kits made of different types of cloths and threads, and possibly some different motes for higher level gear.

For leatherworkers, obviously some different leathers and hides, some thread, and some motes for the higher level gear.

I have found that the endgame guilds dont always have a engineer to put out a bot to repair the raid on the go.  And not having an engineer takes out too much time from the ppl that casually raid during specific times when they can get 25 ppl online to get the job done. 

Having this improvement in wow would save alot of time and allow more ppl to get farther in the endgame content even if its a huge questchain to get to the ability to make these patches.

I for one would definately do this questchain even if it had me running every instance in the outlands to finish it.