I brought this up at Shadowbringers release and got shot down fairly fast with "get better at inventory management".

As a maxed Omnicrafter, I've converted every material I own to NQ and dumped everything available from vendors or low value and I'm still just about managing with 3 retainers. At 2 retainers, you'd no longer be able to craft various items or gear for friends/FC on the go (even at 3-4 retainers you're stretching it), or attempt the Blessed Tools and things like the Skybuilder mats which can fill slots fast with the timed nodes and shooting mobs would choke your inventory. When you're constantly pruning your bags and restricting your gameplay that much to "manage your inventory", it starts feeling like a F2P.

It's definitely time for +1 free retainer, or at least a Materials bank.