Can I still fly domestically with a MO driver's license?
As of 2018-01-09, the short answer is YES but only until 2018-10-10.
See official documentation for full details, but Missouri received an extension and there's some confusing signage out in the wild implying otherwise.
...Starting January 22, 2018, passengers with a driver’s license issued by a state that is still not compliant with the REAL ID Act (and has not been granted an extension) will need to show an alternative form of acceptable identification for domestic air travel to board their flight. To check whether your state is compliant or has an extension, click here. Passengers with driver’s licenses issued by a state that is compliant with REAL ID (or a state that has been issued an extension) will still be able to use their driver’s licenses or identification cards...
..Missouri has an extension for REAL ID enforcement, allowing Federal agencies to accept driver's licenses and identification cards from Missouri at Federal facilities, nuclear power plants and federally regulated commercial aircraft until October 10, 2018...