What are the repercussions of failing to complete KYC on an exchange?
From my own personal experience so far, I do not see any repercussions aside the fact that you don't get to enjoy the freedom that comes with being able to withdraw significant amount of money on daily basis.
There are some exchanges that allow withdrawal up to $1000 per day maximum for non verified users, while verified users can withdraw up to $50,000 to $100,000 dollars or even more..
If you are a money bag trading on the high side, then it's advisable to verify your account to enjoy high limit.
And let me not forget to mention that there are even some exchanges where they won't allow you to make a deposit without verifications, and some also allow you to deposit, but won't allow you to withdraw without verifications..
Most exchanges won't also allow you to trade in the futures/margin market without kyc verification, and if you are a p2p trader, some big exchanges won't also allow you to trade p2p with other users without passing kyc verification.