Good article on the Leica.
The Panasonic m4/3 system has a relatively small 12-35 (24-70 equiv) constant f2.8 zoom that sells for ~$900, and is really nice for shooting street. It has an even smaller 14-45 that's notably slower (f3-something to 5.6) that may be even better. I sometimes think the problem with companies like Leica is that they define what they want to do in terms of lens qualities (the optically best and fastest, and nothing but the best and fastest) even when those qualities have become somewhat irrelevant to the kind of shooting the camera will be used for. If you're making a street-shooter as opposed to a general purpose camera, then I don't really think you need to worry too much about isolating images with narrow depth of field, because that's really not what street shooting is all about. And with current ISO characteristics, there's not much practical difference (for street) between f2.8 and f1.7, unless you really worry a lot about DoF -- you just shoot at ISO 800 instead of 400, and quality will still be excellent. Also, for most street shooters, you really don't even have to go as far as Panasonic did. I do like the range on their lenses, but would be happy enough with a 35-70 equivalent. And that Leica could build -- it just wouldn't necessarily be the optically best and fastest. I'd buy this camera with a short zoom, even at that price, but not with a fixed lens, although I worry a bit that Michael says that the camera doesn't feel that much smaller than an M.
About the lens cap. Another annoying thing about Leicas (I've had both film and digital Ms) is the goddamn lens caps, and this has been a problem forever. I once lost a lens cap, and got in touch with a West Coast Leica dealer who would sell me one...for $28, if I remember correctly. I bought a knock-off for three or four dollars. In any case, somebody once was making rubber lens covers that were actually stretchy, and that you could stretch to put over a lens shade, and quickly peel off when you needed to shoot. I don't know if they still make them, but with this awkward arrangement that Michael describes, it sounds like Leica should have included one with the camera. I live in the desert, and on windy days there's always dust flying around: you really don't want to walk around all day with an exposed lens.
So far, the best camera I've found for street is the Panasonic GX7, which really seems to have been designed for that specific purpose. It's small, has a nice set of short zooms, has a somewhat maneuverable view screen (not completely twistable, but you can push it down so you can shoot from the waist, or crank it ~45 degrees up so you can shoot overhead) and has a handy button that will turn off the viewers (eyepiece and screen) when you're not using them the better to save the batteries. If goes from full-off to first shot in less than a second and the quality is good enough for me. Still, the Leica with its full frame would be tempting...if it had a short zoom.
Leica made its reputation as a PJ/street shooter, and I think they really need to sit down and design a camera around shooting requirements, rather than lens qualities. Those are very different things. At one time, back in the HCB days, the lenses had to be ultra fast because the film speeds were so low -- not because shooters like HCB or Capa wanted to isolate images with narrow depth of field. (What famous HCB or Capa shot does that? There might be some, but off hand, I can't think of any.)