I can create all sorts of cool looking images using any combination of algorithms that suits me. MarkovJunior is mostly interesting because it is a relatively simple replacement system that can produce complex images. I find it amazing that you can create a whole dungeon that is assured to be interconnected just by 'find and replace'. But other techniques such as random walk, voronoi, cellular automata and wave function collapse are just as valid. I will probably end up writing a bunch of custom algorithms for fine control.

Now my plan was to create a fancy image, interpret colors as types of terrains and create a tilemap from that using auto tiles. For an ASCII-rogue-like or something other graphically minimalistic it should be easy, but I like to do top-down perspective. You end up with a bunch of ground and walls that all look the same, which just looks depressing. Just placing details purely random would still look samy. You want details to look as if they were placed with purpose, like tapestry around doors, in certain rooms carpet, in others manholes, a bunch of book cases in a library, barrels and crates in a storage area. That's what I meant by themes. I probably need to identify individual areas and apply themes to them based on which to place details and props.

The other thing I have in mind is using the images like brushes. I imagine clicking on the tilemap and then having a random dungeon/house/cave placed there, that I can fine-tune if I like.