Yes, we do plan on supporting IE eventually, but we haven't decided on
a timeline or exactly what the mechanism will be. If we continue to
use canvas, I expect we would use ExplorerCanvas / google-excanvas. On
the other hand, SVG is also an option; this is similar to VML, which
might make supporting both feasible, if cumbersome. (There's also the
Adobe SVG Viewer plugin.) Compiling to Flash is yet another option,
though then we lose the tight, lightweight integration with the
browser.
Maybe we'll be lucky and IE will natively support SVG or canvas soon!