I think they should open it, and it should not be plugin, but a protocol, as in flash://adobe.com would launch the app/anim/advanced air application/whatever in flash.app / flash.exe or your open source choice for executing flash.
And at this time when you can do everything for the most in html (html5/csse3/js) it just need skills., why should you embed the really advanced stuff flash could do like 3d games etc. For HTML pages, html is the best.
Then I do not need to restart the browser everytime there is an update to flash either, much safer than a forced execution of flash (I use flashblocking), I do not see the reason for a page to have a lot of different flash animations one page, that scenario would usually be just ads.
And you do not need flash for playing video, that era is over. If you are a developer and can not manage to make a cross platform player / solution and a worst case fallback to flash, you should not develop that page.