The problem with Rotangs (at least in past) was that to maintain a seal between the tips of the rotor and the combustion chamber, they needed to keep a film of oil on the tips of the rotor. This is bled from the inside through small holes in the tips I think. Course the oil gets burned off and has to be replaced, so can be expensive to operate and no good for emissions either. A lot of rotarys exhaust smells like a 2 stroke because of it.
Also, because they fire twice as many times through 360 degrees as an inline 4, they use a shitload more petrol, espically in city traffic. Finally, if you flood them (not so easy with the injected ones but aparantly still possible) they're next to impossible to start cause the fuel in the engine washes away the oil seal around the tips of the rotor and hence no compression. Often all you can do is pull the plugs out and wait a few hours for it to evaporate.
Still, a revolutionary engine in every respect, if you ask me

I've heard that mazda have trialed hydrogen powered rotarys, so mabey they have a future...?