I've thought a bit about it, and I think it is a good concept, although the implementation isn't perfect.

Why good?

- Getting btc out of exchanges is good pricewise: it's likely to "transient enhance" upspikes and dampen downspikes, although the effect tends to zero in the presence of real forces pushing/pulling the price.

- Getting btc out of exchanges is good as a warning or preventive disciplinary action for those exchanges who play with the customers' coin, rehypothecating it or using it for investment without telling them or letting have their fair share. It is also good against other forms of book cooking.

Why implementation not perfect?

People in the know already hold their own keys - well, mostly at least. There won't be many of them who move their funds; not enough tomake a difference IMO. As an example, I do have some coin on a few exchanges, but that's not a significant part of my stash. It is a small part of my play money, and it's good for me to keep it there until I get out of my positions and I move them to the freezer.

On the other hand, people who haven't seen the truth in "not your keys, not your coins" (new coiners but not only!) likely have substantial parts of their funds in an exchange. If they join the Jan 3 Proof of Keys "flash move", it will likely be near the deadline. The sheer number of small transactions is likely to make the mempool go crazy. Do we really want that?

However, if the wave of withdrawals is as sudden as I imagine it could be, it could be even more effective against cheating exchanges, so why not? The mempool will get down to sanity reasonably quickly.

Summing up, as far as I'm concerned the jury's still out on Proof of Keys day.