One important fact that transit fantasizers need to come to terms with is that Translink seems to build Skytrain lines for only two goals:
1. Increase regional connectivity of
Metro Vancouver urban centres
2. Replace busses when they no longer can do the job
All current Skytrain lines under construction or consideration follow this pattern:
The Broadway Extension provides connections to the West Broadway portion of the Metro Core and will replace the 99 which can no longer handle the traffic.
The Surrey-Langley Extension provices connections to West Fleetwood, Fleetwood, East Clayton, and Langley City.
The UBC Extension provides connections to UBC, and potentially may replace the future traffic on the 99 which has TBD traffic.
The Purple Line provides connections to Lower Lynn, East 3rd (Moodyville), Lonsdale, Marine Drive, and Ambleside and handles traffic over the Second Narrows which cannot be provided by additional busses/bus infrastructure.
Hastings does not meet these simple standards. There is no urban centre along the length of Hastings (though I can imagine a world where Capitol Hill and Westridge get the upgrade in the future), and Hastings seems to have ample ability to run more R5s and potentially even add more dedicated lanes.
Hastings is not happening in the near term, so it's not worth planning around.