Natures already give you the ability to lower a stat if you want to, though.
The problem with IVs is that in-game, no one cares. They’re irrelevant when worrying about NPC teams. And in competitive, they’re a massive source of grinding that adds nothing to the strategy. Everything has an optimal spread, and 99% of the time it’s straight 31s except for the non-attacking stat. You don’t have to think, you just have to hatch a bunch of eggs. That’s non-fun and a barrier to players getting into competitive, when the games should be actively drawing people into the VGC scene. Why have a system that doesn’t make the fights more strategic but does make people less likely to play?