So there's a new Unearthed Arcana that features skill feats. Taking one will provide proficiency for its relevant skill and if you are already proficient, you double your proficiency bonus. However, this functionality is already provided by the Rogue's Expertise class feature.
Which begs the question, how do these two features interact? If my Rogue has expertise in Stealth and takes the Stealthy feat, what is my total bonus for Stealth checks? x2 (doesn't stack), x3 (proficiency is added twice), x4 (bonus is doubled and doubled again), or something else?