Pete Carroll announced today that Bryan Walters will take over punt return duties, meaning for now, the Earl Thomas experiment there is over or on hold. Carroll said Earl understood their reasoning for making the move, which was essentially that you could tell that it affected Earl's focus on playing safety.
Walters fumbled a kickoff return in Preseason Week 4's matchup with the Raiders, which he lamented as a "total fluke" -- apparently the Kirkland native has never once fumbled in a game, even going back to high school. Ball security is the top priority for the punt returner job, so I'm sure this is a factor that Pete Carroll took into account. For what it's worth, I actually thought that Walters looked very good in his limited chances so it should be a good move.
Carroll noted that Earl is still in it if a change needs to be made, and for now, Doug Baldwin is the primary backup for that role.