Yup. Anyone mining on Nicehash has that loophole too now. Transfer BTC to Coinbase off-chain for free, then do the GDAX loop. Aren't market orders free, though? Don't need to babysit a limit order if you do and you get the spot price. Last time I checked it was, anyway.

You can get USD out of GDAX for free too using this. Well, "free." You pay the bid/ask spread for the liquidity, which is usually very small, especially on BTC.

As for other strategies, use LTC to get into your account cheaply if Segwit isn't online, then sell the LTCBTC pair and repeat the above.