For the PA announcements It's not a terrible idea, and for a short spur line like Alamein it could be feasible, but you wouldn't want the announcements to go on for too long. Especially when you have expresses you might have an announcement sounding a bit like this
"Good Afternoon customers, the next service to depart from Platform 4 will be the 5:03 Lilydale, stopping all stations to Richmond, running express from Richmond to Glenferrie, Glenferrie to Camberwell, Camberwell to Surrey Hills, Surrey Hills to Box Hill, Box Hill to Blackburn, Blackburn to Mitcham, Mitcham to Ringwood, then stopping all stations to Lilydale. Customers for the following stations; Riversdale, Willison Hartwell, Burwood, Ashburton and Alamein are advised to board this train and change at Camberwell for a connecting shuttle service" x 2, then "And always remember to touch on your myki at the start of your journey"
Admittedly that is the worst case scenario, but it is a scheduled express pattern at peak.
Then in the evening you generally have similar announcements for Ringwood-Lilydale and Ringwood-Belgrave shuttles. That's on top of the Camberwell-Alamein shuttle announcements. Especially in the case of Belgrave, their is about 8 individual stations to announce.
I think a suitable compromise would be something like "Customers for Alamein line services" or thereabouts would be ideal. It's short, and is less ambitious in the sense that it specifies that 'Alamein' is a railway line composed of many stations, rather than just a single destination which the current system can lead you to believe.
On PID displays however, like those in the City + Richmond + North Melbourne, It could be very well feasible and probably advised to list all the stations.