As part of PM-912, we plan to remove support for OP_QUERY for all commands except hello (and legacy hello). But it turns out that many drivers (and the server itself) also use OP_QUERY for authentication-related commands (saslStart and saslContinue). Although it is not mentioned in the scope document, as part of the implementation of this project saslStart/Continue are still allowed to be executed with OP_QUERY. The motivation, according to yoonsoo.kim, was that the repl code was still using OP_QUERY and we didn't want to take the time to modify that code. It turns out this helps drivers as well!
Still, there is a small problem that still remains. Some drivers, including the latest 3.x release of the Java driver (which is the most popular on Atlas), execute the buildinfo command as part of the handshake (it's a long story). And this command is also executed with OP_QUERY. So the request of this ticket is to add buildinfo (and it's cousin buildInfo) to the list of commands that are still allowed to be executed with OP_QUERY.