It would be very nice if i could substitute printing certain materials (like oak wood instead of jungle wood or something like that)

This is already a thing; use the /schematicaReplace command. For sub-blocks, you'd use a block state — /schematicaReplace planks[variant=jungle] planks[variant=oak] or such (note that states left unspecified are unchanged, so you should be able to use this on e.g. stairs while preserving orientation).