All updates currently do document storage validation (depth, field name checks, type checks for _id) using mutablebson. We should consider changing this interface to instead accept BSONObj so that pipeline-based updates, replacement updates, and (soon) $v: 2 delta updates don't need to go through mutablebson.

The current modifier-style update system does storage validation node by node (rather than once at the end), so to do this efficiently that would have to change.

EDIT: After more reading, there's a good chance this would cause perf regressions for modifier-style updates. Doing storage validation on BSONObj in the "update with damages" path would likely require us to serialize the mutablebson post-image object into BSONObj so that it could be passed to the validation code. The serialized post image would be discarded, and WT would apply the damage vector. Re-serializing the post image could be a decent amount of wasted work, and could lead to performance regressions, especially for cases where a very small in-place update is done to a very large document.

We should keep this in mind when triaging this ticket.