I really wouldn't hold out any hope of seeing a drop-in flash plugin for Linux/ARM (or any standard OS+ARM). http://www.arm.com/community/s...../adobe.php
says that ARM are working on optimising Flash for ARM (as any Android user knows) but I expect on Android only or a per-license basis for manufacturers of other ARM devices.
The best bet for a flash-based media player would be to somehow get Android onto the chip and then use a flash binary extracted from the Android Flash Player package but that would considerably restrict flexibility when it came to general applications. If I was planning a RaspberryPi-based media player at the moment I'd be looking at Boxee and staying away from Flash (which leaves some questions about the Boxee flash player and how they have enabled that content on the Boxee Box - is it a licensed Flash Player built specifically for the Boxee Box?).
To be honest, above and beyond Flash, even h.264 and MPEG is probably licensed for inclusion into the Boxee box - maybe XBMC and its derivatives might be the better option.
I suspect that when it comes to the realities of creating a homebrew system on ARM any streaming content from commercial providers might become a crunch point when it comes to dealing with the various DRM/CODEC issues which hardware manufacturers like Logitech, Boxee, Roku etc get around by licensing and compiling binaries compliant with a ton on NDA's
(A look at the Boxee sources reveals flash players for i486-linux, osx, win32 & x86_64-linux only, all pre-compiled binaries)