Small status update. I haven't done any real development lately, but now I have good understanding what I want to do in the next version and how it all will be configured.
Most important, it will allow to effectively (from performance point of view) override everything. By everything I mean, in addition to tiletypes, items and buildings, it will be possible to specify different images for all unmined materials, gems, plants, growths, dead creatures, etc. - things that can have tile number/color changed in raws will not be limited to 256 base tiles.
No raw changes will be needed, the plugin will make the required modifications in memory.
Basic mode of operation will be based on folders/files structure named after raw IDs and other identifiers (plus suffixes for different states/flags), eg.
items/weapon/sword_short.png
buildings/bed.png
buildings/bed-dorm.png
buildings/workshops/carpenter.png
inorganic/onyx.png
plants/asparagus-shrub.png
plants/asparagus-shrub-dead.png
plants/asparagus-picked.png
plants/asparagus-leaves.png
plants/asparagus-flowers.png
plants/asparagus-fruit.png
Also, there will be optional config file that will allow to "redirect" these pathnames to tiles in a sprite sheet, and additionally specify some options, for example colour mode (use bg/fg material colors, use fg colour only, use image as is) and transparency of tiles in workshops. Like this,
items/weapon/axe_battle = items,5,0 [=]
items/weapon/axe_great = items,5,1 [=]
items/weapon/axe_toy = items,5,2 [=]
items/weapon/spear = items,5,3 [=]
...
buildings/workshops/mason [222/=.=/=.=]
The bad news is that I don't know when I will have time to work on this...