<i>efficient vector-based animation</i><p>SVG in HTML (embedded directly in the DOM, not an &#60;img&#62;) is all but certain to happen; the SVG and HTML working groups just have to agree on the details.  Of course SVG in an &#60;img&#62; island is possible already, which is what already more integrated with the browser than Flash.<p><i>support for audio mixing</i><p>HTML5 has &#60;audio&#62;, and the rest will come in time, with enhancements to what's there now.<p><i>tool support</i><p>Actually, there are already more Web developers than Flash developers, so I'm not sure this argument holds much weight... but you can be sure there are people working on this very issue for the Web platform.<p>If these and similar issues all that Flash has going for it against the Open Web, then Flash is on the way out.  In a decade, I expect Flash will be as relevant to the Web as Java applets are today.