I think Game will be in a better position If Riot decides to release some agent that are going to give competition to agents who are currently dominating in the agent pool
Duelist:- After the chamber Nerf I think Jett's Pick rate will increase to atleast 50% as She is now better with the operator so Introducing a Agent that can Awp Would be good for the game. Also As we saw due to chamber Pick rate of other duelist agents like Raze and Neon went a little high where teams tried run these agents will now go to single digit Percentage.
May Be introducing a agent that has a Ability like DASH or TP can work.
Sentinel:- I don't know what you guys think about Cypher and Killjoy but I think KJ and Cypher are more static agents like teams can't make creative plays with those agents so Introducing a Agent which is More dynamic can work. I still don't know Why there is no sentinal agent that has a Land Mine abilities where the mine can do a decay damage or stun on the enemies. Also introducing a sentinal Agent with a flash can also work
Controller :- I think this category of agent is balanced as Teams almost play every controller agent except Harbour Which I think will get some buffs in Future will make him good on maps like Breeze and Icebox
But introducing a agent that can be like both Astra and viper would be great like having a Wall Ability but only a Single charge and Having 2 Spherical or Even Cylindrical smoke (Like Cypher cage) would be great.
Initiator:- With Fade coming in the agent pool I think she is Broken and She is must pick agent on every map except Breeze and Icebox. Having a Agent that has both recon and flash ability would be wonderfull also have a grenade ability like CSGO grenade ability culd work