Commercial fossil power stations already drive their stack gas temperature about as low as practical via various heat capture methods, reheat systems, etc. The limiting factor generally is not recovering more energy from stack gasses but the desire to never drive the stack gas temperature below the dew point in that exhaust gas, doing so causes all sorts of negative chemical consequences for the stack itself, pollution control equipment, etc., increasing maintenance cost and reducing equipment life due to aggressive corrosion of stack components and structure. Plants I operated were strictly kept from dropping below dewpoint on the exhaust for this reason, not to mention temperature input constraints for effective operation of some pollution control equipment, you CAN recover more energy from stack gasses, but doing so hits a cost negative and reliability wall.
Always remember that waste heat/energy for a utility station equates to large $$$, if there's a practical way to extract more energy from a given amount of fuel, they are likely there as quickly as they can implement it. But the carnot cycle and other less heat cycle related limitation put up a pretty tough barrier to going further,
Perhaps this is useful for more "pure" exhaust gas or waste heat streams, but I don't see it happening for commercial fossil power stations