Okay, I've completed the highest priority aspects of the second most important gameplay mechanic (such as there is gameplay). (The first most important bit is already kind of complete, but kind of also waiting for me to generate shit-tonnes of content for it.) I also implemented a piece of labour-saving automation for the player that's been bugging me.
Looking at my list, the "must-have" items are looking more and more doable within a short time-scale, while the "would-like-to-have" items are seeming a bit too optimistic. (And there are few things so outlandish and involved I didn't even bother to put them on the list.)
Although, actually, some of these lowest priority items are the kind of things you see in a game, go "Wow! Look at that!" and then completely forget about (or get annoyed at the unexpected complexities they add). Sometimes working to a tight deadline is just what you need to make you cut out unnecessary crap.