Suggestion: Additional badges and limited item crafting
Additional badges
The current badges mostly focus on combat and weapons, foregoing legend abilities and items. Trackers keep statistics, but there are no colourful badges to decorate your banner with if you so wanted to, neither are there any badges for items (healing or combat). The number of uses, the number of damaged healed, the number of healing items picked up, the number of healing items from Death Boxes, the number of shared items, damage done with combat items, distance thrown, distance travelled by Arc Star, time burned by Thermite Grenade, and so on.
Badges could be organised into: achievements, weapons, items, legends, exploration (visiting certain locations, distance travelled, etc.), and more.
Allowing the player to decorate his legend and banner more than just combat and weapons might be a bit more appealing, and perhaps better showing your play style (assault, support, and so on).
Limited item crafting
Additionally I would suggest that 6 Shield Cells could be transformed into a Shield Battery by the player, 6 Syringes into a Med Kit, one each of Shield Cell, Syringe, Shield Battery, and Med Kit into a Phoenix Kit. Ultimate Accelerants could potentially be transformed from 2 Shield Batteries and 2 Arc Stars. An equal trade could potentially be unbalanced so making it slightly more expensive doesn't make it too bad.
EDIT: Considering Replicators are single-use only it would have to be a separate facility, a legend ability, or perhaps created as if you used a consumable. End-game it could potentially have some use where you, but I'm a bit unsure of how it would affect that final balance. It might perhaps be better suited for some legend ability to transform a few items for better ones.
It's a bit lacklustre and not something I've needed myself, just a simple observation from a few players I played with end-game. It might not be a very good idea, but spending a few seconds transforming these items that separately would take far longer to use into a single item taking less time to use, could potentially be useful in the last ring.
It was just a hasty thought after ending up in a similar situation a few times.
If designing a new legend it could be one with the ability to combine consumables, transform ammo from one type to another, perhaps regenerate supply bins (so twice the loot), or even upgrade weapons or generate mythic weapons. I'm not sure if it would be better suited as a controller (there are only four, and perhaps a defensive one with climbable obstacles) or assault (there would have to be some offensive abilities). It actually resembles Loba more than anyone else, providing support by helping other players with resources.