I hate Glocks. They are a one-trick pony, but even I admit they do that one trick very, very well. I've encouraged many, many people to buy Glocks because of the simplicity and availability of parts, although there is less reason to do so now with the M&P.
The funny thing about Glock is that you sort of have to buy into their way of thinking. As one poster above said about the G26, "people shove it in their cargo pocket and call it a pocket pistol." And they are right. Glock owners will conform to the pistol rather than demanding the pistol conform to them. This is why they deal with the crazy grip angle, the fat grip, and the crappy stock sights. And if you don't like it, well: "NEIN! Das Glock est Perfection, Ju est zee problem!"
So I think Glock knows that its market will do just fine if they don't introduce a slim carry pistol. There is a reason why everybody owns a G19. It holds a good amount of ammunition, conceals up pretty well under a loose t-shirt or sport coat, and goes bang when you pull the trigger. For most people who are not enthusiasts, it works pretty darn well. EDIT: Even for people who are enthusiasts, it works pretty darn well.
So I doubt that Glock will introduce a thinner pistol. It would be a solution in search of a problem and lots of retooling when they've already done a good job at making their customers conform.