When most people experience HTML5 SVG/video/audio DOM, worker threads, and DOM 3D scripting that should finish IE off for good.

Most people won't care. Video is so fragmented each browser needs a different codec and so video will remain served by Flash and to a less extent Firefox. SVG is a niche format. Worker threads are a developer feature and 3D DOM scripting is, err, is what exactly? <canvas /> is 2D. What is this mysterious 3d you're going on about? (Oh and dear god but it's slow under Firefox.)