I can't recall where I saw that, but it was on some UK Conde Nast page giving out specs for advertisers.
If there's going to be a decrease in size, I suppose introducing it with the February issue gets it out of the way, because debuting a scaled-down March issue is nothing to boast about, although any change would probably be spun as a deliberate initiative designed to save the earth, rather than Conde Nast finding yet more ways to save money.
In an ideal world, I'd like to see no change in size whatsoever, but the worst outcome would be a change to that god-awful square size that American magazines opted for, back when they were trying to rebrand themselves as 'luxury consumer products'. I think we've passed that point.