Here's an idea, for a cuben-fibre owner to try (I have none, and right now can't afford any).
With a fabric so incredibly light, you can afford to use 50% or even 100% or 200% extra, and this opens up a range of alternative designs and features.
To make a highly ventilating cuben rain shell, you could overlap horizontal pieces of fabric, like horizontal cladding timbers on an external wall. Each strip would be 6? inches tall, and overhang the the strip below it by 3? inches. You would stitch the flaps down at regular intervals - once every 3 or 6 inches? But in wet weather they may get stuck down with water and close up, so you could add some kind of spacer to keep them permanently open.
(Have I explained that well enough?)
For the upper sleeves, and rain pants, do the same thing. But on the lower sleeves, use a plain fabric. This would allow you to move your arms upwards without letting the rain run in. Also on the bum area of the rain paints - use plain fabric, so you can sit down without letting water in.
It wouldn't be waterproof in very windy/stormy rain, and you could take shelter in those conditions.