From MongoDB blog:
MongoDB 2.6 was released in March, 2014 (over 24 months ago). We are now approaching the end of life of this major version, and we will sunset support for MongoDB 2.6 at the end of October, 2016.
Can we get an official word about when does MDG plan to update Mongo version that Meteor ships with to 3.2? Given the EOL coming in October it would be wise to do that as soon as possible, so we don’t end up with an unsupported database. I know that it’s very easy to install your own MongoDB server on dev machine, but not everyone knows that, and most people rely on whatever Meteor shipped with.
PS. I ran MongoDB 3.2 on my production server with Meteor 1.3 and didn’t notice any bugs with this setup.
PS 2. Relevant issue on Github.