Documentation Request Summary:

$isolated/$atomic has already been marked as deprecated, so now it can be marked as removed altogether. The one caveat worth mentioning is the upgrade/downgrade scenario since it's possible to create a partial index with $isolated in 3.4 and allowed to parse in 3.6. The following sequence of steps would crash a mongod on startup:

1. Create partial index with $isolated in 3.4
2. Upgrade to 3.6, everything works fine.
3. Upgrade to 4.0, mongod will fail to start since it doesn't recognize the $isolated option persisted to disk.

Let me know if that makes sense and feel free to follow up if it doesn't!

Engineering Ticket Description:

Since $isolated does not work sharded, and it doesn't provide full atomicity that people likely want when they use it, we should deprecate and then remove it once a better option exists.

This ticket depends on and should only be done after SERVER-8538