Some back of the envelope calculations from fellows I work with suggested that the waste heat from a single gas turbine exhaust could supply enough H2 for 3 gas turbines - so a CC power plant with 3 gas turbines, 2 with standard HRSGs that use the exhaust gas to run a steam turbine, and the 3rd using the exhaust heat to run a methane pyrolysis process, would be the preferred configuration. Slightly less efficient, but 0 carbon emissions. The biggest issue would be running the plant at varying loads - you would need storage for excess H2 to run more efficiently.