Assuming, enough housing could possible be built in that amount of time, one of the first things that comes to mind is that money will be very constrained if that happens in such a short period of time, so things would need to be built to handle massive amounts of people, very efficiently.
This would almost completely rule out all subways, partly because they are so expensive, and partly because they take longer to built than surface infrastructure.
1. Kingsway would become a LRT route, likely with median tracks on a separated ROW, with 80-150M platforms, running from Scott Rd Stn, following existing railroad ROW to 12th St in New West, and Kingsway to Main, either ending at Pacific Central Stn, or continuing to Waterfront.
2. There would be express/regional trains from Pacific Central, using new double-tracks through the Grandview Cut, splitting around Braid Stn to PoCo/Pitt Meadows/Maple Ridge and to Scott Rd/Surrey/Langley/Fraser Valley via SRY ROW. These would likely use 100-250M trains/platforms.
Some combination of one or both of these is already needed within the next 20 years as the Expo Line will be at max build-out capacity by ~2040.
3. Arbutus corridor would become a main passenger rail corridor, providing access from Vancouver to Marpole (connecting with the existing rail ROW to New West), and Bridgeport, where is would split into local LRT service along Garden City Rd and down to Steveston, and regional service, likely along Hwy 99, to Delta where it would split into 3 lines to Ladner/Tsawwassen, White Rock, and Langley.
4. Rail lines (separated LRT or elevated rail) along many of the lines you mentioned, including (but not limited to) Hastings, King Edward/22nd Ave/Kincaid/Canada Way (UBC-Central Burnaby), 41st Ave, 49th Ave, Main, Fraser, Commercial/Victoria, Willingdon, Scott Rd, Granville, Dunbar/Alma, Lynn Valley/Grand, Marine Dr/Keith/Mt Seymour Pkwy, Nordel/88th Ave, King George(to White Rock)
Basically, this map for all longer/regional connections, plus more "local" lines such as along Granville, 128th in Surrey, etc.
I agree with most of your post, with 3 exceptions:
1. Express route paralleling Expo line - I would have this be following the SRY corridor from Langley, across a new rail bridge/tunnel and through the Grandview Cut to Pacific Central. Benefits of this are that the corridor is almost fully grade separated and the route can be shared by multiple services (to Tri-cities express, Surrey/Langley all day express, Abbotsford/Chilliwack regional).
2. The bi-directional loop around downtown serves many local places, but does so fairly circuitously. Who would the main ridership be? People in the West End to Granville Island? Waterfront to the West End (missing much of the central Georgia/Robson CBD)? Waterfront to Main St? That would be well served by the lines replacing the 3 and 8. Science World to Granville Island? Tourists? Basically, I don't see who the main user group for this line would be, because although it serves many places, it would be faster and more direct to take other lines for the vast majority of people, leaving relatively few to use what would presumably be a very expensive line due to it's location.
3. Lastly, as I mentioned at the beginning there would be very little subway or tunneling due to the exorbitant cost associated with it and at-grade or elevated being significantly faster to construct, especially when there would be a huge constrain on time and finances.
Using the SRY right-of-way, which is the former BCER interurban line. With a new rail bridge/tunnel and some additional tracks through the Grandview Cut, it could cross the Fraser and head to Pacific Central Station.