I’d also love to get metal brackets, supports, more metal doors, and that sort of thing – making the buildings look more advanced.
However, I think the Engineer’s place is to create mechanisms and advanced components; fancy decorative brackets could be the role of the Blacksmith. Or we might even get a new class like Artisan or Atelier who creates fancy furniture and building components (e.g. golden thrones, glass products, embossed metal building tiles and hangings, statues/sculptures…)
For the meantime, check out the “slabs with terrain colours” mod – that adds all the natural ore colours to the building palette, so you can build with gold, copper, etc… or at least make it look like you’re building with them, lol.