A number of exchanges have agreed upon a contingency plan should a Bitcoin hard fork take place. You can read the full story here.
Are you going to support Bitcoin Unlimited or Bitcoin Core?
We will continue to support Bitcoin Core as BTC.
Should a fork happen, BTC Markets will make a Bitcoin Unlimited balance available, proportional the the amount of BTC (Bitcoin Core) held at the time of fork. This is subject to appropriate levels of reply protection being met. Without replay protection, we won’t be able to preserve user balances on both chains.
At this time we have not decided if we will be listing Bitcoin Unlimited for trading, but a withdrawal service will be available in the event of a hard fork.
– BTC Markets Support