Before feature flags, FCV checks were done within server code by comparing our current FCV to some FCV constant. Now that feature flags are available, they seem to be a better infrastructure for these sort of FCV checks. As a result, we should consider transitioning away from these FCV checks and replacing them with feature flags throughout the code base. This can potentially be done by banning usages of these FCV constants in C++ code, so that they can only be referenced in feature flag IDL files.

We should start by typing up a proposal for this change and sending it to each of the server & query teams. If we do make this change, we should also send out an email to DB contributors regarding this.