It's a Wonderful Life would be the most iconic Stewart look to me. Any Stewart would definitely be in line with Rainman's own preference for taking on truly iconic Hollywood types with his choices of Audrey Hepburn, Chaplin, Clint Eastwood, etc.
Rear Window would be awesome if he could get the wheelchair down. I'm a Jimmy Stewart fan, but for some reason he's not someone I'm aching to have a figure for. Bogart and Lee Marvin, yes.
Agreed. Fingers crossed he goes back to old Hollywood.