will this 'randomized material' system be tied within the reactions and within the job manager for reactionless workshops?
or are those going to be used just for FB and curses and stuff outside the reach of a fortress?
You may have to explain this question a little more. I'm not sure what "be tied within the reactions and within the job manager" means.
depending on what will be available and how, random metals and stone may affect the fortress jobs.
without considering the availability of random stuff for digging:
bronze colossus leave a stone statue, will 'random metal colossus' leave an usable statue? that is, usable in rooms and in workshop.
magma man leaves obsidian, will 'random molten man' leave usable stone? that is, selectable for use in the stone menu and available in mason/trap/etc workshops
considering the availability of random stuff in layers where it can be dug out:
will those dug stone be available for jobs? will random ores be available for smelting? what will be the use of those smelt ores within the forges? right now, metal using jobs (weapons, armors, anvils, bins) are strictly defined in raws and the job manager allows to create specific metal jobs ("seven iron dagger", but also "smelt copper ore" and alloys)