Back to level themes. I have a plan to create quick versions of unfinished level themes, but even it seems to be hard. I need plans for my plan! I have a vague idea for each level theme, but it's not good enough. I think better way to handle this is plan each theme on paper as I have done for couple of them. Then it's easier to think how to implement features presented in the plan.
Level themes are difficult, because they involve content creation. Yes, that pesky content. I think even seasoned game developers can be surprised about the amount of content needed in a roguelike. No matter how random the creation process is you still need to design it. And the amount of design is multiplied by the number of level themes. On top of that I have ambitious ideas for level themes, most of them with special features.