The market hasn't shifted. It's the same as it has always been. Weapon lights on small EDC handguns are the exception and not the rule for most people who carry a firearm; however, for those like you who want that option, there are already several options on the market. You already admitted to utilizing one of those those options. You also admitted that there are rail attachment options that's allow you to use bigger more bulky lights. Again, there is no reason to change the design, and I doubt S&W will change the design as it's not a make or break feature for most people, but changing the frame and adding a rail will turn even more people off.
Other than that, I suggest investing in a handheld flashlight as you shouldn't be "identifying <possible> threats" or anyone for that matter vs pointing the loaded gun at them anyway. Your thread should already be identified BEFORE the muzzle of your firearm is point at it.
Your reading comprehension skills seem selective at best. Yes there's an aftermarket rail adapter for the Shield, but you give up holster availability, which then means the gun can't realistically be carried.
I think that you fundamentally don't understand how a weapon light should be used in civilian defensive scenarios. Moreover carrying a separate flashlight is not a realistic option all of the time. If the light is attached to the gun then you'll always have it.
In a defensive scenario, you'll only be able to use what you have on you. I do carry a separate flashlight at times, but I can't all of the time.
With home defense, if you *have to* use a weapon light to search, use the peripheral splash of light from low ready or similar... Trigger finger off the trigger, support hand finger on the button. Otherwise it's usually best, where possible, to retreat to cover or concealment and then use the light when/if the potential threat emerges in order to confirm its actually a threat.
In all scenarios, if there's justified reason to point, and if there's time, hit the light just to be absolutely sure the guy has a weapon in hand and not a cell phone. You use the light because you've already perceived a threat and because you have time to confirm the threat before shooting.
If you end up pointing a gun and light at a perceived threat when there wasn't one, that's much better than shooting a perceived threat when there wasn't one.
Activating the weapon light is part of my battery of arms and adds zero time to my draw stroke. It happens *after* I've found reason to draw, after my support hand is on the gun, and before the sights are leveled with my eye.
Of course all of that assumes a scenario where there's time to bring the sights level with your eye. To that point, weapon lights/lasers exist that will automatically activate when drawn from the holster. I have mixed feelings about them, but they exist.
Perhaps not among your circle of friends, but the the market as a whole definitely has shifted. The wide selection of micro 9mms with rails and the plethora of holsters and attachments are proof of it. Those products exist because there's market support for them.