I have seen spoke wheels made tubeless, and i am not referring to the BMW design either (although the BMW wheels do look killer).
it can be done easily enough, but results vary. The nipple area of the rim is sealed with RTV silicone. The stuff is applied from a caulk gun and spread out with a bondo spreader. It takes a fair amount of RTV to lay a thick enough spread to seal everything up, but it can be done, and still weighs less than the tube and flap.
If you try this on your own you take your life in your own hands. I accept no responsibility for anything negative that results from your attempt at this.
You can see how one fella did it at
http://teamincomplete.com/Boxer/boxerhome.html
this guy did a cafe BMW air head bike, but the part that is of interest is the tubeless spoke wheels he sealed up from tube type rims. the whoel build is interesting, and I personally woudl love to get a ride on that monster. it is supposed to be built up even more now, but who knows if he has done anything else with it....
Doc