I feel like the whole notion of Tuesdays/Wednesdays are best for upgrades and Mondays/Fridays/weekends are worst is a function of business travel demand, which is still absent to varying degrees on international routes. I'd venture that the premium leisure demand that has taken its place is a bit more evenly distributed throughout the week, meaning that upgrade chances on a particular day of the week might not be as predictable as it once was.