As the person who added this 7 months ago but now has a bit more experience on OSM, here's my take:
- If it is going to be added, the type should be set to "proposed"
- Now that my mapping skills have slightly improved, I should be able to add it.
- Whether it's going to be built or not? According to https://www.transport.nsw.gov.au/projects/current-projects/mount-ousley-interchange, construction will start in 2024, so it will be built. It did take the NSW govt a very long time, though...