The fingerprint reader is gone - Sony says it would have made the bezel thicker and the company firmly believes the right place for the reader is on the side, that's why it didn't just move it to the front or back.
In Sony's new naming scheme "XA" is basically a letter of the alphabet - the Xperia XA and XA Ultra are in a class of their own, sitting some way below the X and X Performance in the pecking order.