Ok, lets brainstorm some ideas. There is a massive amount of possible tiles that can be overriden, and there is a fairly large list of tags that Japa opened up. How to most sensibly combine them?
It has to be things the player creates, like constructions; furniture and items. For those the player has the agency and can pick the material. Due to a TWBT bug (creatures with transparency on overriden tiles = Ugly) we can't use anything that dwarves stand on; like floor tiles or bridges.
The most sensible from the list seem to be:
BONE
MEAT
WOOD
IS_METAL
IS_GEM
IS_GLASS
IS_STONE
EVAPORATES (ice)
STOCKPILE_THREAD_METAL (adamantine)
THREAD_PLANT (cotton cloth for example)
YARN (dog hair cloth for example)
TOOTH
HORN
PEARL
SHELL
LEATHER
SILK
In addition to that we can use a few jokers: Trick the game into thinking a material has a special tag that we add manually. For example EDIBLE_VERMIN, EDIBLE_RAW and EDIBLE_COOKED are good candidates for iron, steel and bronze weapons/armor, because the metals only exist in bar or item form ingame, non of which are item-types that are selectable for eating or cooking. This way we can cheat a bit.
Now we need to decide which constructions, furniture and items to pick.
There are 12 wall tiles + 1 for fortifications.
There are tons of items/furniture without a subtybe, 36 in total that make sense for this. (Bar, Blocks, Door, Floodgate, Bed, Chair, Chain, Flask, Goblet, Cage, Barrel, Bucket, Animal Trap, Statue, Bin, Table, Armorstand, Weaponrack, Cabinet, Box, Slab, Coffin, Leather, Thread, Cloth, Totem, Backpack, Quivers, Trapparts, Coin, Pipe-Section, Hatch-Cover, Grate, Splint, Crutch, Traction Bench)
And then we have items with subtypes; weapons, armor, clothing, tools, toys, ammo, trapcomps. 106 total, minus food and instruments.
Lets assume we want to make MEAT, BONE, METAL, STONE, WOOD, GLASS and GEM, and maybe a split for IRON, STEEL; SILVER; GOLD; ADAMANTINE. That's 12 sets. Times about 150 items, more or less; that makes roughly 1800 sprites.
I can probably single out quite a few, since no one makes gem quivers, the stone-wall already exists, meat-weapons are pretty pointless... I'd also have to add at least 1 modded workshop that allows the player to make the required materials, like MEAT/BONE blocks/boulders; glass beds or gem weapons, otherwise they can't access the fancy sprites.
I guess in the end it comes down to about 1000 sprites, about 4x 256 tilesets worth. Not too bad.
Edit: Glass walls... a bit boring I guess, similar style as the ice walls, just with little windows with them.