Hm, right. However it /would/ be possible to combine both setups: if disableOtherVillagers is active, it informs the player about the right hiring item etc., just like it is currently doing, otherwise, if not clicked with the right item, it opens the normal villager trade window allowing normal trading..

So IF some server admins should want it this way they would have the possibility configure it to work this way.. however personally I probably would prefer setting it up to work like you suggest it (replacing trading with hiring and informing the player about his possibility of hiring) as well ..
It's just the idea to have both possibilities of setting it up included..