Niantic yet implemented a secret egg changes to Pokemon GO. To be more specific, six common species have been removed from eggs! Plus, 2 additional species have changed rarity.
The Silph Road has recorded all the details on the egg changes and gladly, mostly of the most undesirable Pokemon to appear on eggs are now removed to Eggs. In addition to this, there are several pokemon that increases rarities and they now can only be hatch on 5km to 10 km eggs. All the reports of Silph Road can be seen below.
Here are the six Pokemon that no longer hatch from new eggs:
These pokemon ceased appearing in new eggs at or soon after the beginning of the Grass-Type event on May 5th. Eggs acquired and hatched in the subsequent periods, including the Rock-Type event continued to lack these 6 species.
In addition to the 6 species currently retired from egg hatches, two species became less common:
Dratini - Changed from COMMON to UNCOMMON
Pineco - Changed from COMMON to UNCOMMON
Though both Dratini and Pineco are 10 KM eggs, they were among the most common hatches at the time of our last rarity tier analysis. Today, they are still relatively easy to hatch, and have simply been moved from the COMMON rarity tier to the UNCOMMON tier.
Additionally, Scyther's rarity was unclear at the time of last publication, being equally likely to be an UNCOMMON and RARE hatch. It has become clearer that Scyther was a RARE hatch before, and is still a RARE hatch today.
Here's the new rarity chart now for Pokemon GO as of June 1, 2017:
Source: The Silph Road