Single post in "Pity" Hatching / Guaranteed Shinies

As much as I like the idea, I just feel this would be ineffective or overpowered, depending on how many hatches till you get a pity special. I also feel like it takes away from the fun of the game. E.g. If it was 8192 hatches, assuming worst odds possible for getting a shiny, and no sei days, the chance is (399/400)^8192, or 0.0000000124311844%