Coming from a capitalist mindset here, I think it would behoove investors to only do business with exchanges who have agreed, contractually, to not use customers funds to vote on anything. From the exchanges perspective, if they say they don't want to vote in governance, this should be a non-issue. The market only does business with these exchanges and the others fall to the way side or change their behaviors. Seems to me like a win-win for everyone.
We're already seeing the boost that KuCoin got from announcing that they added Steem and would not use liquid balances to vote on blockchain issues.