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The First Modern Car Without Hydraulic Brakes Is Headed to Production
(www.thedrive.com)
This is a most excellent place for technology news and articles.
But this is the same as just having a split electrical circuit to a brake-by-wire solution. It's only a pseudo-redundant system because you still rely on a single type of mechanical connection to brakes.
Easiest way to design it would probably be by making it a NC circuit so they brake unless they have power to open the brake cylinders.