Originally Posted by
canadiancow
It books "into" I/O the same way AC Latitude upgrades book into R, or AC IKK books into I. Availability is not necessarily dictated by those fare classes.
I have processed SAUA redemptions when the flight was O0 I0.
I don't believe that there is a general rule. Likely depends upon the airline.
Another thing to look at is exactly which fare classes are eligible. On LX, I believe it's YBMU, which can drastically lower the price of an upgradable ticket.
The information is available on the aeroplan web page for each airline.
Other detail: one needs to be booked on the actual flight, i.e. on the operating airline flight number, not codeshare.