Dunno. I asked that very question to someone I know at the company.
He said he'd not heard any rumors of a .45 version of the Shield, but that he also wasn't connected to the Shield project. He also suggested I not hold my breath.
The Shield 9/.40 demand is far out ahead of production, and they'd stock-piled a few thousand units before the guns were even announced so they could release them on the commercial market on the actual release date. They apparently sold faster than anyone expected.
I suspect they're going to remain busy trying to catch up to the demand for the 9/.40's for some time. (Remember that the .45 version of the M&P pistol line was the last caliber model to be developed, and it took a bit longer because of the difference in caliber size/length.
A Shield .45 would require a larger frame, and it's anyone's guess if they could make one that balanced perceived diminutive size against whatever the buying public might consider "adequate" magazine capacity.
Personally, while I wouldn't mind having a plastic S&W .45 of similar size to my CS45, I'm much more interested in the 9mm version of the Shield.
I figured out my preference for the littlest of the S&W 3rd gen 9's when I realized that although I've owned my CS45 longer than I've owned my CS9, and I've fired a few thousand more rounds through the CS45 for range training/practice than I have my CS9 ... I prefer to actually carry my CS9 over the CS45. It's just enough smaller, lighter & handier than the .45 version to be preferable. Easier when it comes to felt recoil, controllability & recovery, too.
The company might well have a Shield .45 project under development, or at least sitting in the wings ... but I'd not hold my breath for it until the demand for the 9/.40 has abated a little.