We're a long way from needing reversible computing, silicon isn't going to get us anywhere near the theoretical efficiency the universe allows us in non-reversible computing. Maybe after we transition to photonics or ballistic electrons or DNA computing or something and plumb that technique to the limits of it's efficiency we can worry about reversible computing. In the mean time, we really only know how to make good computers out of silicon and dark silicon is really only a concern in a silicon context.