Just opening to walk through right . Talk to a good tile setter brick and stone have been used like this for a very long time. Same as doing a shower ceiling. I trully do not understand the need for the porcealin and especailly mixed with crown in what appears to be a very contemporary space .IMO in this style of space less is always more .

What do you suggest be put in for the hallway Center opening? Wallpaper? Textured paint?
So far the fabricator won’t install the slab just cut it. Too risky they said. But my moulding person said we could stick the slab at top, and then use crown moulding on the sides 2” to hold it up in place.

I would never install a slab on the ceiling... It just needs a beautiful light fixture.

You can also use 3d panels

Thanks everyone. So far the best plan I have so far is to put the slab up on the ceiling in that pocket. Hold it there with some wooden stick holding it up. Let it glue and dry. Then take 2” moulding on each side to help reinforce it up. So the slab goes first and then crown moulding on each side to hold it up.

Crown molding to hold glued slab? Beside to be decorative, I don't think it is going to hold anything.

Yeah no fabricator wants to place it on ceiling. So looks like it’s a no go. Will have to do textured paint or wall paper.

You haven't found the right fabricator. Not all that.