Fork choice maximum reversions

[djrtwo]

Pulled from the old ForkChoice checklist at #1053

Maximum reversions: Enshrine dynamic weak subjectivity reversion period into fork choice rule ("second finality mechanism").

@vbuterin @JustinDrake What are the thoughts and reasoning here? Should this still be integrated?

[JustinDrake]

My understanding is that, technically speaking, we do want to enshrine the weak subjectivity period in the fork choice rule, especially in the context of "surviving WW3". Having said that, from a pragmatic standpoint it may be best to sweep this detail under the rug until phase 1+. Indeed, hitting the weak subjectivity period without finality is an exceptional condition which is a) unlikely to happen, and b) would likely be handled with manual intervention. My inclination would be to formally update the fork choice in phase 1 so as to not distract the launch of phase 0. Tagging this issue as phase 1 for now :)

[djrtwo]

Agree with the push