According to The Verge, Apple has confirmed that the SD card slot in the new MacBook Pro models is UHS-II. What this means is that the SD card slot allows for read and write speeds of up to 312MB/s with UHS-II compliant SD cards.
While it would have been nice if the new MacBook Pros support UHS-III (speeds of up to 624MB/s), USH-III compliant SD cards are seldom used due to their expensive prices. Nonetheless, it is still great to see the SD card slot on the new MacBook Pro models!