I'd like to propose that we change this setting, to 0, which means disable HostDB Synchronization. This is an incompatible change, but nonetheless a step in the right direction away from persistent HostDB storage. People can of course still enable it.
Note that changing it to 0, or changing it from 0 to something else, requires restart. It's only "dynamic" if it it's not 0 (which turns off the sync cont).