Some of xDB Cloud environments still run MongoDB 2.6. These environments remain fully supported by Sitecore and respective vendors even though the End-Of-Life date has passed.
Sitecore is planning to bring down MongoDB 2.6 support for xDB Cloud on 30-Sep-2017. On that date, Sitecore will upgrade all these environments to MongoDB 3.0.
Before this date, all xDB Cloud customers are requested to ensure that Solution 1 described above is applied.
Note: A customer can initiate an upgrade to MongoDB 3.0 or higher for the respective xDB Cloud set before this date by contacting Sitecore Support.