There seems to be stories about these new reduced rolling resistance tyres. Are these going to be mandatory? From my understanding, they don't work as well, and make more noise, and increases braking distances? What's the point of that then?

I should add that they seem to equate thes etyres with reducing the carbon output of your car, so I assume that as they have less friction they use less power/carbon. But if they have less friction they are not doing what they are supposed to do. Tyres should have MORE friction not less!!

can you get these in big sizes, or only in 15" / 16" ? I will need to get some new 18" tyres soon, and was wondering about looking into these?

The friction associated with rolling resistance is separate from the friction al force acting between the tyre and the road - commonly called grip. The friction associated with rolling resistance manifests itself as heat, and only serves to slow down the rotation of the wheel. It is quite possible to have a lower rolling resistance without reducing the grip available.