I see the thing with retainers but also I still use 6 retainers and they aren't necessarily packed with gear for glamour, one of them has a ton of weapons I'll never use though, primal stuff, so I still think your idea is valid, maybe make weapon appearances not saved but armours could be saved to this new system? Though I guess then people would wonder why not both. I'm sure a team looking for the pro's and cons of this could find solutions fairly easily.

Worst case scenario SE could make the feature a small extra sub cost. For example an extra retainer is £1.15 or 1.40 euro, maybe the new feature would be a flat £3 per month or something. I still think the idea is more efficient than multiple retainers regardless and has more impact on the inventory issues of FF, so I'd say worth the cost personally.