If Glock ever steals a march on other quality gun makers and does offer a G-43 in that caliber I'd buy one in a New York Minute and sell all my other self-defense pistols.
I'd probably not hold my breath on that happening. It remains to be seen whether they'll even offer a spinoff model chambered in .40 S&W (even presuming they could, with some changes to strengthen the frame).
Even at the peak of interest in the .357SIG (meaning 10 years after its introduction) I was told by someone at Glock that they only produced 1 gun chambered in .357 for every 2500 guns produced, and that was when they were really interested in pushing it to LE.
The Shield 40 was a logical step after the Shield 9, but that's because the design of the frame includes the stainless steel sub-chassis molded inside it, which is further enhanced by being pinned to the steel sear/locking blocks at each end, essentially forming a steel box to lend strength to the frame and help mitigate the effects of recoil force on the polymer frame.
Alas, even S&W didn't see a market for the Shield to be offered in .357SIG. Due to lack of LE interest and sales they finally discontinued the caliber being offered as a regular production item in their standard M&P pistol (although I've been told they'd still make them for a LE order, if received). Just not enough market for a standard production offering. Not when the other calibers are selling strong and well.
You can keep your fingers crossed, though, and hope Glock decides to try and pull a rabbit out of its hat in figuring out how to try and make the G43 withstand the pounding of a .40, let alone a .357.
