I think people are going overboard here. This is what my guess is they have in store for it:

A retainer can be sent to a certain area within a level range. As their level goes up they can gather in more higher places. For example, let's say they have 5 levels: Lv. 1 lets then gather from spawn points in level 1-10 areas, Lv. 2 is 11-20 areas, Lv. 3 is 21-30, and so forth up to Lv. 5. You can choose a few items you want them to specifically look for and as their level increases so does their chances of successfully finding that item. They'll pick up random junk along the way as well of course. Now the catch of this is while a retainer is out gathering their storage is inaccessible to the player and they cannot run a bazaar. The more dangerous/difficult the area you send them the longer they'll be away.

So overall it really evens out, you can have your retainer gather items for you but while they're off doing this you lose the rest of their functions. It's either set up shop and have access to your storage, or send them off foraging. Full/Part time gatherers will still have a job because after all, people will probably only send one retainer out at a time to gather and it's unlikely they'll come up with a big haul anyway. This might just be for potential areas where you've got nothing to sell and might want or need a specific item but nobody's selling it. Send your retainer off to go fetch it for you.