The current listIndexes command displays in-progress index builds by default, but it does not include any information to indicate which indexes are in progress.
The command will report this information with the "includeBuildUUIDs" option, which displays the UUID of any active index builds as its "buildUUID". This option is not enabled by default, and at the time of writing, is not documented.
To avoid confusion for users, listIndexes should just include buildUUIDs by default. We should consider eliminating the includeBuildUUIDs option, or at least making it default to 'true', since the current behavior is pretty confusing. In the spirit of being more explicit, we may also want to consider adding an "inProgress" field, since it might not be obvious that the presence of a buildUUID means that an index build is in progress.
"includeBuildUUIDs" is not part of the stable API, so I think we can safely remove it without having to update the API version, but I'm not sure.