The last two 5D models were announced one year after their respective 1Ds models... To date Canon has not announced a 1Ds Mark IV (it's about 6 months overdue now, if they were trying to stick with their usual upgrade schedule). So, I'd take the rumor of a new 5D Mark III with a grain of salt... Latest rumors about 1Ds4 is that it might be intro'd in two monthd - August 2011 - along with some lenses. Further clues? 1Ds3 is no longer listed at all on Canon's own web store. And it's "currently unavailabe" or on backorder at a couple of the largest dealers (granted, one of them is out of stock with 1D4 too, but the other has that camera in stock and the 1D4 foed appear in the Canon online store, though it's listed there as out of stock at present). It's been rumored to be everything from 27MP to 37MP to 42MP camera. I ain't placing any bets or holding my breath, but the same and some other rumors put the 5D3 out to around Summer 2012, which would be relatively consistent with previous introducitons if we see a 1Ds4 in August.
Sure, it could happen next week, in two months or anytime Canon is ready to launch a 5D3. It also could just as easily be nothing more than a rumor and you might have a really long wait.
You are probably aware, 30mm isn't really wide at all on a 1.6X crop camera such as your 40D or the 7D. It's more of a "standard" lens. It would be the same as using your 50mm on a full frame camera.
About the widest commonly available prime for crop is Canon 20/2.8, which works out similar to using a 35mm lens on full frame (okay, it's slightly wider... equiv. angle of view to 32mm on FF). The 14/2.8 is just way too expensive to buy as a wide prime for a cropper and I wouldn't normally list the 17mm TS-E or 15mm fisheye as options, because they're pretty specialized lens.
My point is just that for crop sensor cameras, you pretty much have to go with a zoom if you want anything very wide.
For what you shoot, assuming your Flickr is representative, a 5D II would be excellent choice and it will give you the cleanest high ISO shots possible with any current Canon model. I think you would find 5DII images can be made at about two stops higher ISO than your current camera, perhaps even more. Should be fine for time lapse, too. I really haven't used it for video at all, so can't advise about that.