Currently there is a huge potential in adding existing perks from other careers and heroes to chaos wastes as boons. There is no reason why f. ex. bardins “Under pressure”-perk should not be added to Siennas boon pool or f.ex. waywatcher kerillians extra ammo passive or blood shot (extra shot after melee kill) to everyone.
Regarding Sienna her biggest weakness is lack of synergy you build up in your build that centers around getting cheaper ranged attacks one way or another. One would think that overcharge vent perks would be cool to get on any Sienna. Famished flames (150% burn dmg, 30% less all else) would fit nicely in challenge chests and would make crafting new builds on the fly fun.
These are just a scratch of all the perks already in the game that would make cool extras on other classes.