If you shield cancel Fiona's wall attack at the peak of the little flip that she does at the beginning, she can actually attack OoS at around the same height that she was before starting the attack because she rises during the flip. This could be useful to fake opponents (for instance, bait them into sheidling the wall attack and then grab or drop down and dash attack).
If you're frame perfect this can also be used repeatedly to maintain Fiona's height in the air for longer periods of time for stalling purposes. This doubles as a taunt because of the goofy "Hahh!" sound Fiona makes every time she wall attacks.
Pulling off the stall is bloody tough, have you actually managed to do it for more than about two reps? Far beyond me.
But it's a really neat application of shield-cancelling, and the most interesting tech Fiona has going for her that I've seen/found so far. The only quibble as to the utility is that the opponent will probably predict the cancel every time, given the wall attack's relative lack of threat.
Fiona has a lot of unexplored stuff, super underrepresented imo. Between her crazy mobility options and combo game I imagine she has a lot of hidden tech. The input for the stall is basically the same as Robin Hood's infinite wall attack at the ledge tbh. It's not viable to run down the timer or anything since it's so technical and at most any height Fiona can wall attack from, the opponent can still jump up and grab her. It's still good to mix up her landing options tho I think, which is nice.
As an aside, her Fiona's air game is dumb. She gets one of the best airdodges, a good air dive, and a fast air dash that stuns. Combine that with her combo potential off her dash attack and special and she has some of the best approach options in the entire cast.