My first reaction was "April Fool" but if it is someone has gone all the way and built a website which is stiil there (1740 2 April UK time).
I'll be interested to see how it works. Firstly, how many people will be truthful about their weight and, even if they are truthful, what happens if the airport weighs you as heavier? Secondly, I don't know if they have any interline agreements with through fares but if they do how's that going to work?