Electrification is an equation. Does the savings made from purchasing electrified rolling stock (which is much cheaper than DMU) equal the cost of electification. Sooner or later, electrification will happen - the only question is when. Of course, if battery technology improves, you might not need wires the whole way.
Imagine it - train goes under wires to the edge of the metro network, and uses batteries to get to Geelong where it goes back onto wires to recharge. Not science fiction - Japanese test train is doing it at the moment from memory.
RRL means the track capacity issue to Geelong goes away - well until you hit four trains per hour from Geelong which won't happen for a while (especially if that's four 9-carriage trains).