My guess is Anderson will be starting in RF to open the season, with Urias at 3B. The video the Brewers posted had Counsell kind of alluding to Turang playing on opening day, which points to him at 2B and Urias at 3B. If they keep Miller, he fills the super-sub role.
They need a backup in CF defensively, and Miller has been seeing a lot of time out there in the last few weeks. He is also already on the 40-man, while Wiemer would need to be added. Given Voit's addition today, those 40-man spots are tough to come by right now.