There's been no official word from Intel or ASUS about how this feature works but it's believed that at least theoretically, it could be used to scale up to a 20-way RAID-0 with a maximum 128GBps bandwidth.
One big catch seems to be that if you want to use it as a bootable partition, you can use only Intel SSDs. The other big catch is that only RAID-0 is supported in default mode, to use other RAID variants like RAID 1 or RAID 5 you will need to buy a special dongle from Intel to unlock these features:
So why would Intel put all this work into a feature and then add a surcharge which could kill its adoption? Intel officials weren’t on hand to say, but the surcharge is related to the enterprise underpinnings of the Core i9 and X299 platform, where the feature is an up-sell. Intel can’t sell it to one customer and give it away to another, can they?