what parts of flash are not open? When flash opened those parts you mentioned? do their knowledge and control of the closed parts of flash enables them to build better tools? how big a lead did they have for their tools when they opened those parts of flash ? Are they still today the leader in flash tools so maybe it's not worthwhile for a competitor to enter?
I really don't know flash in depth , but my guess is that they today have a big advantage in flash tools and moving to html5 would seriously reduce their advantage.
The source code of the Adobe Flash plugin, if nothing else.
Incidentally, that does bring to mind one possible Hail Mary that could work: Open source the Flash player(s). Whether the open source community could fix performance issues on Linux and OSX depends on a lot of things, but they could certainly fix some things that would make it less aggravating.
(Since it's probably impossible to open source as-is due to licensing agreements it still might not work; depends on how much of the plugin is still left after you've removed those bits.)
Flash's ActionScript engine, for instance, was donated to opensource and subsequently used to make Firefox faster.
(Adobe Flash Player includes licensed codecs from Fraunhoffer, On2 VPx series, H.264, more... Adobe can distribute them, but cannot license them for redistribution by others.)
If they open-sourced it, it would be difficult to standardize. With a major release every 12-18 months, it's already difficult to drive adoption (takes about 12 months to get > 90% user base per version).
I will agree - they might want to consider open sourcing the Linux version. I know nothing about Linux so I'm guessing it's related to trying to support the "anything-goes moving-target many-flavors-of Linux" issue.
I really don't know flash in depth , but my guess is that they today have a big advantage in flash tools and moving to html5 would seriously reduce their advantage.