From DF Talk:
Toady: Well I mean the hardest things are always time travel and stuff and that just needs a bigger disks. But I'm not sure they really care about time travel that much, it'd be cool to get the fluids in there, because I want giant lakes of blood and stuff and all the sand and that kind of thing. But as with any 'favourites' question it always just comes back to what I was just thinking about like ten minutes ago ... I'm absolutely horrible at these kinds of question, it's the worst thing in the world for me. Some people can rattle off their favourite movies and colours and things but I totally suck when it comes to that kind of thing.
Capntastic: It does seem that there's going to be ... I think you mentioned some sort of time skip ability with growing crops, the ability to make time pass quickly which wouldn't be like the sleep command.
Toady: Yeah, it's one of those things ... it's not quite like a holy grail of time travel that's impossible, but it's one of those tricky things we've avoided. One of the reasons the sleep command works in the ridiculous way it does is because you don't have to abstract time if it's just pressing period for you eight thousand times. So it's going to be a little tricky, but you have to have it, you have to be able to skip a season and let the world deal with itself. That's one of those things; there are a few things on the dev pages that are like little walls that we're going to crash into. Entity populations is one of the ones that'll take a while, abstracting time is another one, so I kind of want to plan my development around those, and not start them so soon that we don't have a lot of the serious bug fixes out of the way, so that I can work for a couple of weeks on entity populations and people aren't going to be - I'm not sure it'll take a couple of weeks, but just theoretically working a few weeks on entity populations - and then not have people being like 'well I wish you would have made it so that when my dwarves make turtle crafts they don't turn into fireballs and destroy my military' or whatever bugs are still there.
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So again like 99% of your hundreds of threads, it's something that has been discussed or planned. You should work harder on making actually useful threads, like you agreed to do last time you were wondering why people were getting mad at you.