(libv commented on their thread: http://www.raspberrypi.org/archives/2221#comment-34981
maybe he'll follow up with a blog post at some point).
So to start the GLES implementation is on the GPU via a firmware. It provides a high level GLES RPC interface. The newly opened source code just does some marshalling and shoves it over the RPC.
Why is this bad?
You cannot make any improvements to their GLES implementation, you cannot add any new extensions, you can't fix any bugs, you can't do anything with it. You can't write a Mesa/Gallium driver for it. In other words you just can't.
Why is this not like other firmware (AMD/NVIDIA etc)?
The firmware we ship on AMD and nvidia via nouveau isn't directly controlling the GPU shader cores. It mostly does ancillary tasks like power management and CPU offloading. There are some firmwares for video decoding that would start to fall into the same category as this stuff. So if you want to add a new 3D feature to the AMD gpu driver you can just write code to do it, not so with the rPI driver stack.
Will this mean the broadcom kernel driver will get merged?
This is like Ethernet cards with TCP offload, where the full TCP/IP stack is run on the Ethernet card firmware. These cards seem like a good plan until you find bugs in their firmware stack or find out their TCP/IP implementation isn't actually any good. The same problem will occur with this. I would take bets the GLES implementation sucks, because they all do, but the whole point of open sourcing something is to allow other to improve it something that can't be done in this case.
So really Rasberry Pi and Broadcom - get a big FAIL for even bothering to make a press release for this, if they'd just stuck the code out there and gone on with things it would have been fine, nobody would have been any happier, but some idiot thought this crappy shim layer deserved a press release, pointless. (and really phoronix, you suck even more than usual at journalism).