I'm sure I'm not the first person to ask for this, but it would be massively helpful for redstone builds if blocks that serve the same function could be treated the same in material lists, either as an option for the client to toggle (based on some pre-existing lists of interchangeable blocks), or as a way schematics could be made. For example instead of a schematic requiring specifically gray concrete, it could ask for just "Solid block". It's very annoying having to either modify the schematic myself to match the blocks I'm using, or just ignore when the schematic verifier tells me that a bunch of blocks are incorrect (which might lead to mistakes if you don't realize that a block does need to be the specific one that the schematic asks for, or if you miss actual errors as a result).

This has indeed been requested many times, and there is a "valid substitutes" system planned for this.

I don't necessarily like the idea of complicating the schematic file itself with some kind of substitute data, but we'll see if that becomes an option too... it would then likely like inside the Metadata tag and obviously be optional data.

So mostly this would be a user-configurable system that affects how the renderer and the material list and verifier check if a block is "correct". If it's also supplied from the schematic, then it would just be a pre-loaded "preset" or configuration to that system.