I think this article is fascinating.
I've always advocated using CD(M, H or B)A for two reasons: 1) that's four of the most common letters in the English language (which, as the article mentioned, doesn't mean jack squat when the producers are making a point to avoid those letters), and also 2) with ten of the most common letters accounted for, even lots of blank spaces provide valuable information. With large expanses of letters unrevealed, you know you have to click your brain into an alternate mode, and start thinking about compound words and awkward letters like Js, Ks and Ws.
G, H and O make sense since they show up in a lot of adjectives (like "rough" and "tough"), which the writers have liked in recent years.
If this really is the trend, I wonder if contestants will catch on and start migrating towards it.