Summon both retainers at once

[Iscah]

That's not what I mean. I mean having, say, 4 Retainer windows up at once to look through 4 different retainers. Being able to drag and drop items between them.

I think if they could implement multiple retainers at all, two at a time would be more likely. That's enough to transfer items between them without needing the middle step of taking it out to your inventory first.