Not a bad idea. In fact, I would love to see more depth to the repair system, and your suggestion certainly beats mine in terms of being fair to casual players. I think the idea of the "secondary" class capable of repairing having to use two mats would maintain a decent balance.

The only argument I can come up with against this idea is that it seems most appropriate for low and mid-level gear. In the current game, high level gear SHOULD remain the purview of and keep exclusivity of high ranking classes. That is, a Rank50 weaver item should only be repaired by a weaver.

BUT, if they do add class-specific and rank-restricted gear, I think that adding two repair classes to every non-specific/non-restricted piece of gear would be totally awesome. One of the advantages of using general gear is that it is generally easier to repair. Use specific gear, go to specific people.