Re things like glass tile. The Kerdi instructions say to call the tile manufacturer AND Schluter to come up with a suitable workaround, if it is possible. Since the requirements can be quite stringent, and you want a warranty from both the tile and the membrane user, that collaberation is required. Chances are, you can get a suitable, warranteed install, but you need to ask. Since the exact solution may vary, they require the collaberation consulation before approval. Just like you may need approval from your local building inspector if you want to do something outside the norm. If that's too much trouble, use a different product.