Agree that investors with funds on Binance etc should not lose funds, however these funds are now stuck because of the powerup by Binance etc.
There are a few options:

1. Contractual agreement with exchanges not to power up customer stakes;
2. Code based changes to delay witness voting for 2-4 weeks after a powerup;
3. Fork the exchange stakes into a trust account that would release the steem directly to the investors with proof of ownership.