I think you nailed it on the ceramics. Pretty sure they are looking at falling ceramic particles in the tower to capture and transfer the concentrating solar.
Silicon carbide would work up to 1800 C. Various refractory oxide ceramics could also work.
This whole approach needs direct sunlight, so it's not great for a place, like Europe, where it's often cloudy. It would be better for deserts, like in Chile, Namibia, or maybe the Arabian Peninsula.
It's not great for a production site. But for engineering tests, you can do a lot of stuff with no sun, and the occasional clear skies are used for sun testing.
But in this case, maybe it is enough to have just a small part of the central reaction vessel handle 1,500 C? Maybe using ceramics?
Or can you 3D print an Inconel chamber with builtin cooling channels that makes it possible for the Inconel surface to handle the incoming heat?