I'd honestly just make a board with a constant air step spell except it follows the rules for flying (but you can slow down if you have contact with the ground). It even has rules about using it over water. Then maybe provide a list of "tricks" you can do with a successful Fly or Acrobatics check.
Air Step is nice, but the only part that really works for me in regard to hoverboards is "you ignore difficult terrain that is less than 1 foot high, you do not trigger effects based on weight (such as a pressure plate), and any creature trying to track you through areas you crossed with this spell takes a –10 penalty on its Perception or Survival check to do so". Thanks for the recommendation.
Would a hoverboard be significantly different than a flying carpet?
Ha, I thought about that. Really wanted some skateboard like tricks like grinding and ramping though.