Ignoring the movie's quality, The Polar Express came out in 2004 and blew me away when I saw it in IMAX 3D. Maybe it wouldn't hold up post Avatar but when the layered snowflakes came down over the WB logo I was pretty gobsmacked.

I can't find it now but I remember some interview where he said all it takes is time, money, and attention to detail to get post-conversion to like 80% of native 3D quality it's just that no one wants to do that.