Yeah, you're right, Wayne did say that Scott was interested in shooting another non-Alien movie in Aussie. And the Australian Outback can easily double for the American Old West.
But I saw a couple of tweets a few weeks ago, one saying he was in Mexico doing location scouting and another with a photograph of him with some Spanish army officials saying he was currently scouting over there for Wraiths. Could be that he will use a selection of settings from different countries and do the studio shoots at Fox Studios, Sydney.