This hoverboard doesn't have any unlockable upgrades.
Bubblegum is the seventeenth limited hoverboard in Subway Surfers. Like any other hoverboard, it protects you from crashing for 30 seconds. When crashed, it will explode and need a few seconds to recharge. It has no special ability. It has a pink background with the text 'POP!' written in light blue on it. On the backside it says '!'.