The Proba missions are technology demonstrators. The main goal of Proba-3 is to demonstrate precision formation flying [1], which would enable large instruments in space without the need for large mechanical structures and complicated deployment mechanisms. Even in the age of Starship this could be useful.
The coronagraph is one example of an instrument that benefits from formation flying, but its actually considered a guest payload on Proba-3. Benefits of formation flying include being able to adjust the distance between the two spacecraft to block more or less of the Sun disk. Also in traditional coronagraphs the occluding disk is held in place with struts that obscure parts of the corona.
Other applications that could benefit are telescopes (radio, optical, X-ray), interferometric SAR, in-space inspection and servicing of existing satellites, to name a few.
