I agree with many others that this thing definitely has a niche (and by Niche, I mean as I, an Ecologist would use the term, as in, it has a place in the world).
Can definitely see its niche as a running/racing/FKT type product.
-For me once I start pushing hard enough, there is very rarely enough rain/cold/wind to make me need a fully waterproof jacket. My Tachyon Windshirt does fine. Literally has to be 0-5C and wind blown cold rain for several hours on end. Problem also negated with waterproof mitts and a light beanie (that I happily let get wet-gets wet with sweat anyway).
-Go a bit colder again, and by then the precipitation is starting to get dry. Greatly reduced need for complete waterproofing, breathability more paramount.
I can definitely see its usefulness for poncho/cape users. Especially in heavier weather when you are more likely to, by chance, spend time in camp outside your pitched poncho/cape. Especially if you are with another person/group and you want to spend a little bit of time socialising in camp with them (and outside of your shelter). If pushing very hard, the type of hard where a poncho/cape is unweildy and slows you down slightly, this jacket could be an option in that scenario where your speed is great enough that you are still warm.
In bad conditions hiking solo it probably works better than with a group. Why? Because you choose your pace. If you need to push harder or run to stay wet-warm, you only have to motivate yourself to do so. You don't have to make everyone else run with you. There are only a couple of people I hike with that move fast enough for me now, if hiking with anyone else (eg taking Scouts out, or my toddler), I need a waterproof layer or else I'd get cold waiting for them. That could be my Gatewood Cape.
The Slabs option is expensive though for the weight. I was hoping to see something more like 3oz.
Also agree with other's comments that a strip of WPB on the upper of the arms would be handy. Particularly forearm.
A Tachyon Anorak with a slightly longer, waterproof zip, and WPB Cuben panels would be pretty cool.