I would really like to see a silverlight framework compatible with 64-bit IE.
I know the argument that IE32 is the default browser on 64-bit Windows, but there are a lot of us that change our default browser to IE64, and for some of us geeks that like to type "iexplore www.xyz.com" from the run prompt rather than click IE32 from the menu end up with IE64 running. Supporting IE64 when Flash does not would also be a good marketing edge.
Microsoft has been making a big push towards 64-bit computing, especially considering that many of the server applications are now only available as 64-bit. I like the move to 64-bit computing, but until Microsoft does it across the board how can anyone else be expected to do so?