Yesterday was a big day for GM's regional brands of Holden and Opel, both previewing new flagship siblings, the Commodore and Insignia Grand Sport respectively.

Between Opel, Holden and Buick, extensive work has gone into GM's global E2 platform in order to satisfy three distinct markets--four if you include the Vauxhall rebadge-- but curiously, Buick stayed home from the party.

We asked Buick why it didn't preview the upcoming Regal with its kin, we were told the timing simply didn't make sense for the U.S market. Fair enough, that leaves us to do some informed assuming.

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Opel announced the Insignia will shed a significant amount of weight, 385 lbs to be exact, which joins a three-inch longer wheelbase, a two-inch-plus growth in overall length, an inch lower roofline and almost another inch of girth. Expect the Regal to sport similar, if not identical growth in exterior metrics, but Buick's extensive use of sound deadening may reduce weight savings.

Holden confirmed yesterday the soon-to-be imported Commodore will initially be offered with a choice of three engines: a 3.6-liter V6, a 2.0T and a 2.0 diesel. The V6 will be hooked to GM's new 9-speed automatic gearbox and a twin-clutch AWD system, while the pair of two-liter four-cylinders will be FWD exclusive.

This revelation squares with information provided by an internal Buick source earlier this month. The well-placed source claimed the Regal would add V6 power this time around in response to rivals, in addition, he claimed Buick is considering adding a diesel choice three to five years down the road. As for the twin-clutch AWD system, Buick already sources such a system from GKN Driveline for use in the new LaCrosse and Envision models.

The transmission question is a bit more difficult, no Buick model currently uses the 9-speed gearbox making it impossible to guarantee the Regal will offer the jointly-developed transmission.

What can be guaranteed however is the addition of a wagon variant, Buick confirmed such a model to its dealers in May of this year, before the source confirmed Buick would add a crossover-style wagon next year called the TourX. Yesterday Holden announced it would also receive liftback and wagon derivatives.

Final development phase: The Opel Insignia Grand Sport is still heavily camouflaged. Opel's new flagship will celebrate its world premiere at the 2017 Geneva Motor Show.

On the technology front expect Buick to offer an 8-inch configurable display, featuring Apple CarPlay and Android Auto, along with 4G LTE Wi-Fi and potentially GM's next-generation head-up display. This will join an elevated suite of safety features the Buick brand has become known for, like Surround Vision, automatic front braking, rear park aids, forward crash avoidance, lane keep assist, lane departure warning, blind zone alert, cross traffic alert, and vibrating safety seats. How Buick decides to package this content will not be clear until later in 2017.

Unfortunately Opel's cutting edge IntelliLux Matrix LED headlamps will not cross the Atlantic as they remain illegal under U.S regulations.

The Regal should make its global debut at the 2017 New York Auto Show in April of next year, before arriving on dealer lots toward the end of 2017 as a 2018 model.