When upgrading to MongoDB 7.0, we faced several severe issues with Slot-Based Query Engine (SBE), and we had no way to opt-out of using the SBE. Refer to Support Case https://support.mongodb.com/case/01207868.

It would have been very nice if we could have opted-in to the SBE after upgrading to 7.0 on a per-query basis, i.e. by setting a "queryFramework" parameter on the query ("classic", "sbe", or "auto"). If this feature existed, it would be nice that if a given query is not possible to execute on the "sbe" it falls back to using "classic" without an error (hence this is more of a "queryFrameworkPreference" than a hard requirement.)

We think this could be very valuable for helping customers on MongoDB 4/5/6 upgrade to 7. As we understand that SBE will be rolled out to more use cases in the future, it would still be nice to have this in MongoDB 8.0 and beyond.