I don't know how an exchange take this kind of step if they don't want to scam people's. Suddenly asking KYC verification and disable withdrawal without KYC verification is clear symptom of scam users. They should implement withdrawal limit for Unverified user and it should continue at least couple of week and they should notice their user about thei KYC verification.
Every exchange will implement KYC requirement one by one, as crypto is moving completely towards centralization.
I think this is the only way left for exchanges to handle the KYC thing, block users funds > ask for KYC > if yes, OK > if not, permablock.
If an exchange want then they can provide options for users to choose, but it is not they forcefully want users to perform KYC. The world is not free.
If I recall correctly then bittrex made the biggest noise about this KYC thing... now it's cold like ice.