CIAO is still a first-class citizen in VFX.
The job performed by Classhook is now performed by the recogniser system. See the CIAO and CLASSVFX sources to see how this is done. One of the benefits of recognisers is that we have been able to reduce the number of DEFERred hooks in the system.
Another benefit of recognisers is that with careful use of vocabularies and search order control, it is possible to switch OOP packages in and out of the system. This enables different OOP packages to coexist. The recogniser source code is in Kernel\Common\kernel.fth.