A new free items and rare Pokémon encounters for referring their friends. With the addition of 12 km eggs, there are now five different variations of eggs in the game that players can hatch for a chance at a Pokémon, both rare and not-so-rare.
The problem is, the odds for which Pokémon are available in which egg variant are not visible in the game itself. Trainers have, therefore, been requesting a change like this for some time now. The Pokémon GO community has gradually figured out which Pokémon hatch from which eggs, sharing the information online. Typically, for a player to see which Pokémon can hatch from which egg and at what rate, trainers would have to search for different online sources (some of which are more accurate than others).
A tweet from the features and events coming to Pokémon GO but this change was not one of them.
However, while some trainers have received this news well, others have questioned the usefulness of this feature. The tweet only mentions, "rarity level," but not hard percentages. The official hatch rates are still missing, which has been an issue for Pokémon GO players for some time. Some trainers have offered anecdotal evidence and a few have even come up with some rough calculations, but there has not been any official numbers published. Pokémon GO has repeatedly given trainers increased chances to encounter rare Pokémon, but even in those instances the actual odds still are never disclosed.
Meanwhile, other trainers have taken this opportunity to ask Niantic to allow them to discard less-promising 2km eggs to clear space for 10 and 12km eggs, giving them better chances at rare Pokémon. Niantic has never hinted at adding such features, but there was also no hints that it would let trainers preview Pokémon hatches in Pokémon GO, so only time may tell.
Source: Niantic /Twitter