It's a trial balloon. This will cause enough heart palpitations over at what-used-to-be the Democratic Party to make Scalia look like Hunter Thompson when Bush promotes him to Chief Justice.
Another possibility: The president is already going in another direction, but is releasing this story that a particular candidate is "under consideration" as a "thank you for services rendered." This is done when professional sports teams are cutting down to the "short list" to fill a coaching vacancy.
I can't imagine that Bush wants another confirmation circus involving Justice Thomas. Yet conservatives owe him a lot.
I don't think that it will be Scalia, either. Scalia would have to repeat the hearing process while another candidate for associate justice goes through his/hers. Too many chances to have liberals gum up the works.