No they couldn't have. Not with the way the display is currently engineered. If they made the glass in
front of the display matte, it would diffuse the light being expelled by the
LCD panel as well as light coming from external sources. The only way they could offer a matte display is if they got rid of the glass panel in front of the LCD panel altogether, which would result in a thicker/bulkier display; and Apple is not going to do that.
The glass panel now supports the whole display structure the way a winshield in a car supports the car's unibody
[source]. Its not as simple as you think. The only reason we had a choice in the old MBPs is because all structural rigidity came from the the aluminum structure
around the display.