Can we pause for a moment to talk about Offical/VGC/Doubles?
Topsy Turvey is pretty much a Sword of Damascus for any stat based team; it's effect on the metagame will be stunning.
Yes, it'll be stunning because it's an awesome move that won't see any use because Malamar is just too slow and frail to take advantage of it. Many boosters increase their Speed either through a Speed Booster that Baton Passes or Dragon Dance, making it easy for them to outspeed Malamar (if they don't already). And due to Malamar's lack of bulk, he'll probably get stopped by the sweeper as well.
There are a few niche cases where he can use it, such as against Reuniclus or Clefable, but that's about it.