Did you notice? With the latest stable version 1.43 of the ProSim A320 you can now import flightplans from Simbrief directly into the FMS. So no need to type in waypoint by waypoint into the MCDU anymore! This is how it works.
1. Generate your flight plan in Simbrief.
2. On the INIT-Page press "REQUEST*".
3. After a few moments you will find the INIT page filled with the date from Simbrief.
4. Same with the flight plan on the F-PLN page.
5. Also most values on the Init Fuel Prediction page are already filled in.
Many thanks to the ProSim development team for adding this useful function!