Good questions. At this time evolution would be of interest in predicting whether there might be earthlike planets in that solar system. Predicting anything beyond that now is pure speculation. Evolution itself as a tool of science or refutation of evolution is of interest to some people, but you would have to ask them why.
I'm not sure I follow. Did Darwin make mention of earthlike planets? It would seem to me, if anything, evolution might predict whether life would arise on these other planets- not predict the existence of the planets themselves.