RER carriages are not compatible with Sydney as they are 112 metres for 5 carriage sets. Each carriage is about 22.4 metres in length and can supposedly hand 1300 passengers but this is mostly standing and not sitting. There is only 34 seats per carriage.
RER operates multiple formats on it's various lines: 3 door SD, 4 door SD (IIRC), 2 door DD like Sydney, and 3 door DD.
I'm taking this way too seriously, but this is how I see a NWRL extended suburban could (and in my view probably will) be implemented:
This is the 3 door DD design from RER Line A (busiest). 6 rows per deck, 4 decks per car for 24 rows of 3+1 & 3+2. It's better to have most of the seats facing the same way, as leg room can be provided beneath the seat in front, but that's not needed in Paris as it will be in Sydney.
For the NWRL it'd be 4 rows of 2+3 per deck as the car length is shorter, and the doors have to match the platform screens. There would also be fewer staircase platforms - as the trains will necessarily be shorter.
How much shorter? Can't tell. A Sydney DD now is 4400mm, the NWRL might need to be as short as 3800mm.
The train can be made shorter in various way, all of which have a cost trade off, usually in passenger comfort.A) Ceiling height
. The obvious one. I believe A is currently 1800mm or 5'11", just enough to ensure 6' tall men have to duck their heads. Reducing ceiling height further is great, as this distance counts twice! (Up to 50mm x 2 = 100mm)B) Allowable Clearances.
By stiffening up the suspension, more frequent track inspection and/or reducing top end allowable speed (oh my gosh, in Sydney?) the allowable clearances could be reduced from 150mm to 100mm safely. (Up to 100mm)C) Offset Standing and Seating Floor/Ceiling Positions.
This is a variant of the US "gallery car" design, where the top deck seats are at the height of overhead luggage racks, not the ceiling of the walkway. Note the (exaggerated) potential discomfort of the person in seat 5.
Like quiet carriages, in this #MeToo era we could have "Women Only" decks (a bit like India), and thus lower the ceiling height on that top deck even more!
If C could "comfortably" be as much as 300mm (most people are 400mm-450mm shorter seated than standing), but beyond that you'd be looking at 2+2 seating on the top deck.
Up to 400mm saved.D) Composite Materials.
Reducing the thickness of the floor and ceiling with carbon fibre/composites rather than steel construction. This will be needed anyway to reduce weight
to get up the 1:20s. (Up to 100mm). Adopting all of these measures to their maximum, you could reduce the height of a DD vehicle from 4400mm to 3700mm !!
Sydney has a long (and sorry) history of compromising passenger comfort and safety to comply with the evolved "standards". Don't think it can't happen, despite the best efforts of the Metro's designers!
BTW, I'd be curious to know the lateral dimensions of the NWRL Metro. It looks awfully narrow to me, though I was under the impression the system was speced to use the same lateral width, so when lines were converted they wouldn't need to rebuild *all* the stations