So I think if possible to be added there should be KitPvP Killstreak rewards.
My suggestion for milestone/rewards are here : ( Feel free to comment your kill milestone/reward ideas )
5 Kills: Normal golden apple
10 Kills: If Possible the speed 2 effect for 25 seconds
15 Kills: Sharpness 1 Diamond Sword
25 Kills: Strength 2 effect for 20 seconds
50 Kills: Sharpness 2 Diamond Sword
I don't think there is a need for more rewards after 50.
My suggestion for milestone/rewards are here : ( Feel free to comment your kill milestone/reward ideas )
5 Kills: Normal golden apple
10 Kills: If Possible the speed 2 effect for 25 seconds
15 Kills: Sharpness 1 Diamond Sword
25 Kills: Strength 2 effect for 20 seconds
50 Kills: Sharpness 2 Diamond Sword
I don't think there is a need for more rewards after 50.