Perhaps it'll kill Flash a bit quicker considering the amount of Kiosks and Internet cafes running Firefox+Flash on Linux.
You must not watch many videos in your browsers then outside the odd one on Youtube. The reality out there is that Flash is still the main choice for delivering video. Flash is a necessary evil. It may be dying but for many it's still necessary and its removal from Firefox removes significant usability for its users.
And if iPad sales are any indication I don't think it's as big a deal as you make it out to be.
If I write some software that costs $999 and only works on HP/UX, it's not "Fuck Microsoft" or "Fuck Apple". It's "Fuck me."
I think they call it cutting off your nose to spite your face.
Flashblock plugins are ridiculous by requiring you to blacklist or whitelist flash domain instead of web domain. The former happens to be on CDN and suddently you can't do it :(
So the only thing non-Chrome-using Linux users will miss out on are things that use the new features of Flash introduced after that date.
Plus the older hardware I run Linux on can barely show a 288p Hulu video, with lots of stuttering, even though the machine can play videos twice that resolution flawlessly in any of the native video players.
Before recentish versions of Firefox, a Flash crash would bring down the whole browser.