Why do we need this? The way that Flash has diminished in significance since high-quality browsers on smartphones and tablets emerged is a good thing. The web is better with Flash gone completely, not dragged along through compatibility layers.
First of all, good old backwards compatibility. There's large codebases still written in Flash, or perhaps things that are in Flash that will never get updated ever again (browser games being a big one), and people would like them to work even after Adobe's dropped out. It also turns out that reimplementing Flash in HTML5 gives you a great idea of what's missing if you want to tell developers to just use HTML5. There…
It's a fair point that wanting to retain the ability to run this content after there is no (working) Adobe plugin is desirable, but is the browser the best place for this? We don't demand that each version of an operating system is able to run all old application software for that OS; the preferred way of being able to do this is through virtualisation, and I'd argue that's probably a better way to do this, too.
> There has been quite a lot missing from the web standards that Shumway helped pushed through.
…such as? (I'm genuinely interested; I wasn't aware of this)