The goal of the game is to be a simple yet realistic! (Loving the art style - I'm an artist and done some pixel arts but not in a pro level) having an option to lock the board on skater for the sake of doing FS flips smoother will look unrealistic. Locking the board on skater's foot will be great if we have impossible in-game. You can lock either nose or tail except the mid (balance) so that the option is for the impossible only.
BTW, I just thought if we can control the flick while in mid-air or at the pick of an ollie we can do late flips ( I don't know what button to press again to make if flip) e.g. nollie late flip you have to nollie first then put the kickflip (still in air) then press whatever the button you have to press to make it flip (maybe the RS since you're setting your tricks here and the fun part is you still need to press land to land the trick) - I know that RS is used in resetting your trick input but I can't think of any buttons :D
You can check some of my artworks: https://www.behance.net/ninoalecsc3b3