Actually I hadn't noticed that, that would suggest that the Sheng Li is
a much stronger slate, you may get away with thinner / no ply?,
certainly one to ask them.

I doubt it would make much difference. I presume the purpose of the plywood
is to make the floor solid enough that the tiles don't ping off when someone
walks on the floor and flexes it. I doubt the wear qualities of the slate
would affect this, although a good quality flexible adhesive might be
indicated.

Christian.