According to this article, Senna will be getting a prestige skin
Surrender at 20: PBE Preview: True Damage Senna Prestige Edition
3D League turnarounds — PBE update High res: Heart Seeker Jinx
PBE News
Surrender at 20: 10/29 PBE Update: Senna, the Redeemer, True
Surrender at 20: 1/27 PBE Update: TD Senna Prestige Splash & More
League of Legends PBE: True Damage Yasuo Prestige Edition Revealed
Prestige True Damage Senna Skin Spotlight - Pre-Release - League
Surrender at 20: 2/22 PBE Update: Splash and Skin Tweaks