I feel like a new game wouldn't be announed through CoroCoro alone. If it's being shown in this month's CoroCoro it will almost certainly be shown before in some capacity. That's what they've done since BW2 (and HGSS actually, I can't remember BW1's reveal structure). BW2 was shown via Pokemon Sunday (as was HGSS), XY was shown in the special Pokemon Direct, ORAS
was clearly meant for E3shown in a teaser uploaded by Pokemon's youtube channel the day of an investor's meeting
If it's getting shown this year I'd bet either really late this month or somewhere in November, with CoroCoro possibly (but not guaranteed, I don't believe there were any hints towards BW2, XY or ORAS the month before the reveal) hinting as such.