I'd be surprised if the zero'ing out of R-space has anything to do with ex-Europe latitude fares. No R space seems to be opening even at the clearance windows, and I'm seeing many flights go to the gate with half of J available for gate upgrades. Not sure what that's about.
I'd assume redemption latitude fares were a driver, given how much they have been promoted on blogs and how many more customers they're accessible to. But that would explain zeroing out R far in advance, but not the fact AC isn't pushing anything into R at the clearance windows (on any flights/routes I've checked in recent weeks at least). I can't really see what the reason for that is.
It's plausible they want to make non-R/hidden bucket upgrade space available to ex-Canada latitude fares, and not ex-Europe ones, and I can hardly blame them. I am usually out $1900 for a latitude return ex-UK, but ex-EU it seems $1400-$1500 is common. That's just unreasonably cheap for all the benefits of latitude plus instant upgrade months in advance.