FWIW, I've just successfully withdrawn from Mercatox.

Here's what I did.

I first went to Etherdelta:

https://etherdelta.com/#KIN-ETH

Opened account, which doesn't really create anything except a public/private key pair on the ETH blockchain. Please make sure you really really copy down and don't share your private key. That gave me a public key, which you can verify here:

https://etherscan.io/token/Kin?a=0xcdfab7c8bcabda6a4e5be4a07fb8682f0360ee9e

and also here:

https://deltabalances.github.io/#0xCDfAB7C8BcAbdA6a4e5be4A07FB8682f0360ee9e

As you'll see in that link, I've transferred 1572650 KIN out of Mercatox.

Transaction costs were 10000 KIN ¯\_(ツ)_/¯

To transfer out of Mercatrox, I went to https://mercatox.com/wallet, chose KIN, and went to Withdraw. I entered the full amount I had, and as target address I chose the address I had created on ether delta (the 0xcd... from above).

After a short while, I saw a transaction-ID on Mercatrox (https://mercatox.com/wallet/transactions), with TX info at the end of the line, which was a link, which leads to etherscan.io (see above).

Nothing showed up in myetherwallet.com though. While waiting, I also went to

https://www.myetherwallet.com

and entered my private key there. It equally showed up 0 ETH, but choosing KIN on token balances in the lower right corner, I could see my KIN.

After 30 minutes or so, the same value of KIN was also visible on ether delta.

So in summary,

1. I cannot confirm that Mercatox does not allow withdrawals. It worked, and it was relatively fast.
2. The transaction cost was 10000 KIN or at the time of this writing 0.0007 BTC.
3. To transfer the KIN out of Mercatrox, create a public/private key pair on the ETH blockchain, write it down well, and then withdraw to the public key.
4. Use one of the options mentioned above to verify and see that everything worked - and to trade onwards.

HTH,

M