Fine in theory, but becomes an issue of practicality, since most GA sections are the result of inadequate time for the placement of a successful neuraxial anesthetic. Usually there is one IV, and often multiple medications to administer. Utilizing the ETT to deliver an inhaled anesthetic agent can streamline workload considerably. Yes, there are ways around this such as drawing up the induction dose of propofol in a 60 cc syringe, using a push to go to sleep, and then slapping it on a syringe pump if available for maintenance. But, you know, the tube is already there.