SD card logic levels
You are correct, if you look at any of the SD card manufacturers' specification, such as Transcend, Toshiba, and SanDisk, they all specify the same voltage range you gave in your question: 2.7v to 3.6v.

So you should be fine interfacing to these cards from your GPIO pins using 2.8v levels without the need for any level shifters, and of course you will want to provide power (Vcc) to the card also using the same voltage (2.8v).