I've got gases partly reimplemented, they aren't displaying properly at the moment though.
I'm also putting in some of the infrastructure for randomized material properties. To explain:
One of the basic ideas of the game is that you encounter liquids, gases and even walls with unusual properties. They might be bouncy, or sticky, or flammable, or explosive, or poisonous, or have any of a number of other possible attributes.
Here is my plan for implementing this.
First, there is one of each type of substance (fluid, gas, stone) that is not random, but is otherwise boring. For fluids this is water, for gas this is "breathable," for stone this is "inert." My idea is that this substance is the most common of its type in each world, except maybe in the weirdest areas, just to keep down player confusion. (If everything you touch immediately explodes it doesn't make for a very interesting game.)
There are also a number of other predefined substances. Sand and oil are the two major types of these we've seen to date, both holdovers from World of Sand.
Each world also bears a difficulty value, which increases as the player explores more worlds. As difficulty goes up, at world generation time the game will randomly switch out more of the stock substances. So a game might not have sand, but another fluid. It might clump like sand, or it might slide around the ground, or it might slowly eat through stone, etc. Higher difficulty values also make it more likely that dangerous attributes are selected. Later on it would be possible for each substance to actually have two such attributes.
My problem here is: will this make for interesting gameplay? This is the biggest question of the design. My hypothesis is that it will if the player is given a limited number of ways to figure out what substances do, akin to the rogue like scroll of identify and Nethack's many ID tricks. I think this should be balanced so that players can't test out *everything*, just some things, forcing him to put up with whatever special attributes other things turn out to have.
Even if it's interesting, will it turn out to be enough to carry the game? The exploration aspects, the navigation and treasure seeking, and the resource management game of making efficient use of your equipment, all of these things together are what I consider to be In Profundis. If that turns out to be fun by itself then we can make an initial release and add in stuff like fighting/communicating with aliens later. If it doesn't, well then we might have to add in other actors earlier rather than later.