AMD said they want to update their drivers to support it, but Nvidia cards should be faster due to specifically being designed to support it.
If you’re planning to release a product that people will install onto their own machines, you should not use the feature, it will only work on very very high-end GPU’s and isn’t going to be something that most of the market can use for years. That’s one of the reasons why VXGI was removed from UE4 before it was released, because many people don’t have the hardware to run it and stuff like the Xbox One couldn’t run it either.
The main use for this would be to render images and video, where you wouldn’t have to go through the light baking process anymore and you’d be able to get really high quality lighting. Also, as far as availability, it’s not going to be in the engine until version 4.22 so it’ll probably be end of the year/early next year before people can start messing with it.