This change causes the server to log the following message, including a dochub link:
The $isolated/$atomic option is deprecated. See http://dochub.mongodb.org/core/isolated-deprecation
The $isolated/$atomic option is being deprecated because it will be superseded by true transaction support which we are planning to release in 3.8 and 4.0. (The current plan is that 3.8 will support single replica set transactions, whereas 4.0 will support multi-shard transactions.)
The dochub link currently redirects to https://docs.mongodb.com/manual/core/read-isolation-consistency-recency/. When transaction support gets released in the future, we should probably change the link to point to text explaining that you should use transactions instead of $isolated/$atomic.
Do we still have $isolated/$atomic in the reference manual? If so, this page needs to indicate that this feature is deprecated as of 3.6. [nope, we already removed these pages and references]
This doesn't work now anyway, esp. in sharding, and maybe with new yielding.