I literally created this account just to second skimthetrees - basically neither I nor Z guarantees SAUA.
My own personal experience for BR55 coming up: Called in to EVA ticketing office to make sure that the first segment from ORD to TPE (BR55) is in B class. EF shows I = 0. EVA ticketing office confirmed that Z=1. Rolled the dice and booked the ticket anyways. Went on Aeroplan SAUA website and luckily, upgrade confirmed right away for 25K miles. Checked back on EVA website under my reservation and I was upgraded to RL and was able to select seat.