Proactive Chassis Control was one of the defining features of the original McLaren Super Series, the interconnected dampers (which removed the need for conventional anti-roll bars) delivering a spooky level of ride comfort and control. For the next Super Series that's been updated to Proactive Chassis Control II, with one or two interesting new features...
Finding a sideways McLaren shot is quite hard
Let's start with the drift mode. We have to. In McLaren parlance it's called "Variable Drift Control" and will allow "even greater involvement for a driver who wants to fully explore the dynamic ability" of their car. It sounds like a finely adjustable ESC system rather than something actively designed to yob around with - the driver uses a touchscreen to swipe up or down the intervention level - but it's quite a bold decision for McLaren to make. The phrase "additional enjoyment" has even been used.
More sensibly, PCC II now has 12 more sensors than before to read inputs from the road and monitor the tyre contact patch. This information can be processed in milliseconds and the appropriate damping force applied. Again the Comfort, Sport and Track settings are available, with McLaren promising "the optimal balance of cornering grip, dynamic response, and comfort to best suit the individual mode".
What this actually means both objectively and subjectively for a car that was already incredibly competent and engaging remains to be seen, but we're not far off: the Geneva show is a month away. Expect a few titbits from McLaren before then also. Your move Ferrari...