I share some of your skepticism but this is a very different card from wraithling fury. Wraithling fury is very one-dimensional, no wraithlings, no fury. But If you have wraithlings you can get instant value exactly where you want it and use it immediately with the downside of being dispellable.
This card wants a completely different kind of deck. I don’t think it is suited to lurking fear/dying wish style decks. The last thing you want in a lurking fear deck is for your cheap ramped dioltas/reaver or whatever to be turned into a vanilla 6/6 because of a ping and then cleanly removed, basically giving your opponent an extra silence (although, yes, the wraithlings spawned by reaper would be nice to transform).
I think traditional swarm might be able to get away with it thanks to gloomchaser/zyx bodies surviving skorn and reducing the odds of your dancers/priestesses getting transformed, but just how awkward it is depends on certain interactions. Like, if someone plays skorn vs your priestess + wraithlings + this thing does your priestess turn into a 6/6 and spawn no wraithlings to replace everything that was cleared on the board? That’d be some pretty awful anti-synergy. I think this card has more synergy with a more zoo-y swarm style including a lot of the extra body cards swarm likes and cards that have opening gambits but weak bodies, not in any existing meta decklist.
Very well designed, I think. But overall I’m just not sure it’s good enough to see play.

like Battle Pet Rok, low cost - w a big body