QEMU has a lot of interfaces (like command line options or HMP commands) and old features (like certain devices) which are considered as deprecated since other more generic or better interfaces/features have been established instead. While the QEMU developers are generally trying to keep each QEMU release compatible with the previous ones, the old legacy sometimes gets into the way when developing new code and/or causes quite some burden of maintaining it.
Thus we are currently considering to get rid of some of the old interfaces and features in a future release and have started to collect a list of such old items in our QEMU documentation. If you are running QEMU directly, please have a look at this deprecation chapter of the QEMU documentation to see whether you are still using one of these old interfaces or features, so you can adapt your setup to use the new interfaces/features instead. Or if you rather think that one of the items should not be removed from QEMU at all, please speak up on the qemu-devel mailing list to explain why the interface or feature is still required.