We have been hard at work at making mongo+rocks v3.0 production ready for parse environment. Most of the work was done here: https://github.com/mongodb-partners/mongo/commits/v3.0-fb-hack. All TODOs are addressed and all features and APIs implemented.
All of these changes were tested on Parse's production workload (using flashback tool: https://github.com/ParsePlatform/flashback/) and so far the results are pretty good (especially on the write side).
Because of tedious testing, I feel comfortable asking these changes to be merged into v3.0 branch. We would like to use v3.0 branch to build and deploy mongo+rocks into Parse's environment (instead of maintaining our separate branch).
Please let me know if you have any concerns or questions.