DP for anyone interested, since I've been following this thread for a while and nothing really made sense, the last post relevant to me was in March and it was pretty annoying to filter out the misinformation. Btw, thanks to Gengar it was your confident post that made me pull the trigger and you were right all along.
Booked: Today, July 3
Travel: January 2019/February 2019
SAUA program: Aeroplan, 25k points per way
BR 9 to upgrade to BUSINESS in this itinerary: YEG - [YVR - TPE] - SGN
Z = 8, I = 0, but agent confirmed Z is what mattered. ExpertFlyer only shows I, you have to call in to get Z availability
Hold time at 13:00 UTC-5: 30 mins to North American reservations number for Z availability check
75 seconds between clicking buy button on evaair.com and upgrade confirmed on Aeroplan site (to be fair I was probably too quick that if the upgrade declined I'd be freaking out)
Original fare booking classes: YEG -> YVR in S, YVR -> TPE -> SGN in B, SGN -> TPE -> YVR in Q, YVR -> YEG in K. YEG segments on AC.