Here's something that shouldn't surprise anyone who's been paying attention: Cadillac has been dethroned as Detroit's biggest-selling luxury brand. The brand that supplanted it? None other than another of General Motors' premium vehicle brands, GMC.

Combined, GMC's Denali and AT4 sub-brands have so far outsold Cadillac for the year, according to analysis from Automotive News. One component of that - Cadillac's waning influence in the luxury car market - has been on full display for a few years. Sales have slid slowly but steadily since the brand's most recent peak in 2015, despite several new product launches in the fast-growing crossover segment: the Cadillac XT5 in 2016, the XT4 in 2018, and the XT6 in 2019.

But the other component - the rise to prominence of GMC's AT4 and Denali sub-brands - is more of a surprise. Together, the sub-brands account for some 40 percent of GMC's US sales for the year so far, and while there might not be universal consensus regarding whether they count as true "luxury" brands, their vehicles command an average transaction price 30 percent greater than the industry as a whole.

GMC's Denali sub-brand on its own "would be a very, very successful luxury brand," Dunan Aldred, Global Vice President of Buick and GMC, told reporters in September. "We're not doing this by discounting or trying to go to the lower end. We're staying true to the vision of being the only premium brand that occupies this space."

Of course, GMC is set to receive another image boost with the launch of the pure-electric GMC Hummer next year. Even though Cadillac is, officially, at the fore of GM's electrification push, with vehicles like the Cadillac Lyriq crossover, Cadillac Celestiq sedan, and three others set to launch in the coming years, each of those vehicles is arguably more niche and unapproachable.

Reading between the tea leaves, it doesn't take a huge leap to conclude that GM will likely introduce still more pure-electric GMC vehicles in the not-so-distant future. If the Detroit automaker hopes to make electrification work in the US market, it would be foolish not to.