Thanks to Pokémon GO dataminers such as Kelven and Gamepress, new information has been found in the game files. An update will bring some new features to Team GO Rocket, including new red eggs.
No details have been released yet, but we'll update this article as soon as we know more about how many kilometers it takes to hatch these mysterious eggs. It would be logical to think that Shadow Pokémon will hatch from these eggs given the color matches the eyes of Shadow Pokémon, but we'll see!
Shadow and Purified Pokémon will have better stats and do more damage than other Pokémon, so it's worth keeping hold of them — despite being good battlers, boosting them costs a fair bit of Stardust.