Because Adobe will be writing a closed-source module distributed in a binary form, you'll end up with the exact same situation as with plugins IMHO.
Only a subset of the available OS and processor architectures will be supported.
Flash was designed years ago and even though everyone wants it to die, we're still feeling its pain.
Designing a similar solution in 2014 is just asking for trouble for the next 10-20 years IMO.
Oh, and you're giving up the opportunity/right to audit the code that runs on your devices.
Flash attempted to do everything - what we're seeing from it now is just the last few use cases for which it has not been replaced with HTML5 - and the solution is for the single use case for which HTML5 is a bad fit - reducing the bloat, enabling performance improvements and massively reducing the size of the TCB. Ultimately it's about as good as can be got out of html5 video.
Only a subset of the available OS and processor architectures will be supported.
Flash was designed years ago and even though everyone wants it to die, we're still feeling its pain. Designing a similar solution in 2014 is just asking for trouble for the next 10-20 years IMO.
Oh, and you're giving up the opportunity/right to audit the code that runs on your devices.