I did not read the paper, but from the article; probably not. So the E8 idea is stab at a quantum field theory of gravity. On the other hand these amplituhedron idea seems to be 'just' a different idea to calculate usual qft calculations easier. The only connection which may be there is, that apparently the amplituhedron idea can be turned on its head and then serve as a new way of looking onto qft. And this may or may not lead into a interesting direction for quantum gravity theories.