lets say if you had all DoH lvl 50, and for example it wasn't required to change into your lv 50 GSM to repair jewels you can do it as WHM, it would make you be as good as npc mender but you can offer a better price.

there's at least 100 players with all DoH lvled in each server, if Repair request required the menders to carry Dark Matters and only required not switching changing disciple as long as he/she have the required DoH's lvled, then I think it would work out fine, if players realize they can save on repairs and 1k to 500gil profit to be made per repair and you can do all of this within a click, i'm pretty sure it will catch on.