Niccol will face new challenges as he takes over the struggling coffee giant.The news that Chipotle (CMG -2.78%) CEO Brian Niccol has jumped ship to move to Starbucks (SBUX 0.53%) sent shock waves across the restaurant industry. Niccol has had a successful tenure at Chipotle with rapid expansion, revenue growth in the double digits, and procedural changes that addressed the setbacks that hurt Chipotle in previous years.However, Starbucks presents its own challenges. Howard Schultz has been Starbucks' only t ...