I'm still waiting to get my M8, so maybe I shouldn't comment on the lack of a wind lever, but here goes anyway: Years ago I shot a lot of film with the IIIf, M2, and M4. I never missed the wind lever on the IIIf since it didn't have one. I gripped it in the usual way and used a wrist strap for security. With the M2 and M4 I still used a wrist strap, and though I did wedge my thumb behind the wind lever, I didn't depend on the lever for security.
One valid function for a wind lever is to give the shooter control over the noise involved in cocking the shutter. In Vietnam in the mid sixties, and for about a year after I got back to the States, I did a lot of shooting with a Canon 7, which was a great Leica knock-off with a Leica-thread screw-mount lens. The Canon 7 had a titanium shutter. I've listened to the MP3 of the M8 shutter signature you can download from dpreview.com. The shutter sound itself seems almost identical to what I remember as the Canon 7 shutter sound, but since you can listen to the MP3 at any volume level you choose, the MP3 doesn't tell me anything about the volume of the shutter noise. What it does tell me is that the shutter rewind sound that follows the release seems a good deal louder and is much longer than the sound of the shutter itself. For "street" shooting in quiet, less then friendly interiors it really would be nice to be able to cock the shutter slowly and quietly.