Those for Geelong could catch connecting services to West Werribee which was not built but a part of the RRL programme. (The Coalition decided not to do it).
Alternatively a customer could change at Newport assuming this could be accommodated.
For airport line (Tullamarine) I can see scope for a dedicated train service between Geelong and Tullamarine either with a connector at Sunshine or near Sunshine or via Newport to Sunshine (on existing good tracks upgraded).
Thoughts about using Newport path again?
Geelong trains could again run via Newport under fast rail