I want to shed more light into Remove implicit approval chilling upon slash. by kianenigma · Pull Request #12420 · paritytech/substrate · GitHub.
This PR has been open for a while and is part of our efforts into redesigning the slashing system. For the sake of transparency, we actually wanted to merge it a long time ago, but we decided to wait until our proposed design for the “next” slashing system is ready, and then move forward.
The Kusama incident was just some extra catalyst to merge this ASAP and propose it to Kusama (and later on, Polkadot).
In short, this PR removed any kind of “automatic-chilling” for nominators. Validators are still disabled until the next era as they get slashed.
In short, the main function of this mechanism was to protect nominators. As we have evolved and have nomination pools now, entities that want to be idle, and expect to “be protected” should move to being a pool members. Nominators are scarce spots reserved for active entities who are monitoring the system, and respond to event like slashes quickly (and in an economically rational way).
The main flaw of this mechanism was that the way it was originally implemented, even if a slash is canceled, the chilling is not. This has historically been a major pain point. See: Full Slash Reversals · Issue #6835 · paritytech/substrate · GitHub
Weighing the benefit of protecting nominators, and the drawback of damaging validators, we argue that this “automatic chilling” is not worthwhile.