11
Destroy the Evidence
(mtgzone.com)
I wanted to hit a planeswalker and the creature it created, but this notably hits Fable of the Mirror Breaker, Wedding Announcement, Gruff Triplets, and some other non-walkers.
I'm pretty sure this works under the existing rules and you can "remember" a token's creator, but not 100%.
Yeah you're right, it's just too much overhead. The examples below create the tracking requirement when those cards are played, this would require that you always track every token from the start of the game forever.
Could definitely work in Alchemy though.