The exact details of Translink's BRT plan has been quite fluid while they have been figuring out how a the new type of service fits into the existing network within budget constraints.
While they previously called for BRT ASAP for the corridor
their BRT page currently shows that the current plan is to extend the R2 Rapidbus to Metrotown while the BIRT program studies the corridor. Presumably this means if RRT is found to have a higher cost benefit ratio than BRT they won't invest in any BRT infrastructure on the corridor.
Pure speculation from me, this change may have to do with signals from a higher power that an ultimate solution to the corridor could happen sooner than later.