The electrification to Salisbury will rule them out of further service on even the Outer Harbour line, once there is no way into Adelaide and no access in/out of the Dry Creek depot which doesn't have 25kV knitting. But that work is not coming soon by any conventional definition of the word 'soon' – it's scheduled for 2017-18 by which time the Jumbos will be well and truly gone..
One other factor in the "when will the Jumbos be retired" equation is timing of the next big shutdown on the rail system.
"What big shutdown" you ask?
The Torrens-to-Torrens part of the South Road upgrade includes building a new rail overpass at Croydon.
The various DPTI websites don't mention specific dates, but recent editions of the industry publication "Construction Industry News" refer to mid-2015 as when the serious construction phase of the project will begin.
I'd suggest building the rail overpass will be one of the first parts to be tackled.
Given DPTI's past record in closing rail lines and running substitute buses at any opportunity, from winter next year we may well see:-
- Outer Harbor and Grange lines closed between Adelaide and Woodville.
- Trains running only from Woodville to OH and Grange.
- Bus shuttles between Woodville & City.
- Rosewater Loop back in use for empty trips to and from Dry Creek.
With a few more 4000-class EMUs delivered to the Seaford line and reduced demand for railcars for Outer Harbor and Grange trains until 2016, the South Road Upgrade may be what eventually kills off the Jumbos.