OK then. Here's my idea. In order to fix the dead creatures being displayed as ASCII tiles, I've created this set of generic "tileset creatures".
Instead of being assigned a CREATURE_TILE based on the first letter of it's name, a creature will be assigned a tile based on it's general body shape. It's a very crude method, but it has some pleasant side-effects:
1. Out-of-view and dead creatures aren't ASCII any more.
2. Vermin, fish and other small creatures can have graphics now.
3. Engravings of creatures are no longer ASCII tiles.
4. If you don't like immersion-breaking creature graphics, you can disable them and get these simpler tileset creatures.
5. Mod developers can use tileset creatures as placeholders until they get proper creature graphics in. All they have to do is change the CREATURE_TILE of a critter to reflect this system. No new art needed.
6. Tileset artists can use GemSet raws and create custom tileset creatures instead of drawing all of the creature graphics. I like to think of this as an abstract middle ground between ASCII and full-blown creature tiles. Like CLA.
7. For modders, there are 19 empty slots left for tileset creatures.
8. Lastly, this system frees up a lot more tiles for tileset artists to use. There used to be some oddballs like floating guts and creepy crawlers that shared graphics with non-creature objects, but now everything uses the alphabet.
The only downside I could see to tileset creatures is that they require TWBT. Obviously, trying to use a tileset creatures in a text tileset will render your text unreadable. Oh, and if I'm confusing anyone, these are not meant to replace the current creature sprites. They're there to give the game something to fall back on whenever it cannot display a creature's sprite.