Of course there's the issue of artwork... when are you gonna hire me Toby? XD
I'll hire you when I actually get paid for the work I've been doing for the past years. ;P
And yeah, it's not particularly difficult to make characters wade: Multiple layers are already supported (how else would trees overlap you?) - but it's really obvious when you just walk into a body of water and all that happens is that the bottom 3/4 of your body disappear. Now, I could decrease walk speed and whatnot, but the point is, it'll still look rather cheap. I'd need to add at least splashing effects, perhaps some ripples - and that's a whole lot of work for something that'll perhaps only be used once.
It's not that I can't draw; I think after doing all this I know quite well that I can pretty much draw anything I want. It's more an issue of my time, and what I do with it. :3 If you're volunteering to add in stuff, that's great, maybe at some point it'll be a community project (the map editor and user maps are a start for that), but except for very few exceptions, I can't shell out a lot of money for something that not only doesn't earn me anything, but also costs me a sizeable amount of money (since I do need to pay for the servers, every month). ;P