I do hope they have plans for managing retainer inventory, especially considering you can have up to 4 now. I'm fairly certain (although unrelated) they plan on making it so split items in retainer inventory can get merged. If you split a stack, and then sort, it takes up 2 slots and does not merge. I had 1 retainer reserved for reagents and ingredients, and the other one held all the other craft materials. With 4, I was able to split them even further. I also keep a piece of gear in my inventory/retainer inventory, so the 1st page is always "clear" when I add new items. If they don't fall into a stack, I look into it (usually means I'm starting a new stack, or put wrong material on retainer).