Yeah, I should have been more clear. My understanding is that for some years, the hydraulic circuit for the left rear brake was paired with the right front brake (long before ABS, even before power brakes, me thinks). And the right rear with the left front. This was an advancement over the previous braking (hydraulic) circuitry in which all brakes were lost if the single braking circuit were lost. Or even the scheme in which the front brakes were lost (along with most braking) if the only hydraulics remaining after a failure were the rear brakes. That's all good with a four wheel braking system. So...what about the design of hydraulic circuitry of a Elio?
Ah. Correct on most cars. The diagonal system was considered an early safety device, rightfully so. When you started seeing cars with two well master cylinders, you also saw separation of braking ability, either front to rear, or diagonally.
The portioning valve valve gained value when it also "closed" the fluid flow through a line "if" too much fluid flowed to fast! If is still used in some systems and works well, allowing braking from the remaining brakes at the wheels. Some braking systems are very intense, having this system inside the master cylinder even.
My guess, and it's only a guess, is this will also be a part of the inline brake line to each wheel, in order to give you two braking points, if one point fails. Speed sensors at each hub will be used as part of the anti lock system, as well as traction control. The system is very safe, and the price of having it has fallen greatly, as a lot of companies can, and will, supply what is needed.