That's indeed cool. Also device change events -- that's something we've had problems for a long time... USB headphones have their own devices, so removing one in the middle of a Flash experience would kill sound (and sometimes the whole application) until it was restarted. Same with any other plugin, I'm assuming, although I haven't tested Unity/Silverlight/etc to see if they're constantly pooling the list of devices or what.
AFAIK sound wasn't part of NPAPI before and plugins had to use platform APIs, so any sound problems were Flash's fault alone. Even so, Flash is hardly the only program that behaves badly when hotplugging sound devices so you can't really fault them too much.
Speaking of Flash problems, another one I want fixed is keyboard focus handling; specifically how keyboard navigation between HTML and Flash is impossible and browser keyboard shortcuts won't work when Flash has focus. Also, finally killing the windowed/windowless mode distinction will also be great.
So awesome to see Adobe/Google tackling on this.