Be careful about pledging anything.  Sun is trying to get presumably binding concessions in writing without having to do anything himself.  Gradually chipping away the witnesses negotiation tools.

Also if the powerdown is only a week or even 4 weeks and an account should be compromised by a hacker-it would seem that freezing accounts should still be on the table to protect private property.  Instead of a week before the account starts being drained by an attacker, it can be drained in as little as 12-48 hours.

You need to lock down his stake.  Otherwise he'll come in and powerup again and do what he wants when he wants-including destroying the steem chain when he sees fit.  Work to Substitute his steem stake with SMTs that are coded do the same thing as steem-except vote, and burn the ninja mined coins.  It'll be Sun's job to find a market for his SMTs.