The open source drivers will have video and will not be doing decryption so I don't think there will be any legal concerns.
Not sure what you mean about repro-ing a closed source driver issue on open source to get support -- that only works if you switch to the open source driver. There are pretty good support forums for the closed source driver (Phoronix for example) and the request is normally "post your logs" not "repro on an open driver".
On Xorg mailing list, they won't hear about problems involving proprietary driver. For AMD/ATI users, it may be hard to decide if the issue is a fglrx problem or an Xorg problem.
If Phoronix can be used (an advertised) as a single point of support for AMD/ATI problems, then users should be fine. In this case, Phoronix should redirect the queries to Xorg mailing list when needed.
We're trying to keep the driver choice simple. Most distros will include the open source driver, so that's what we expect people to use by default. Users would upgrade to the closed source driver to get specific features or performance not available in the open source driver. OEMs shipping SKUs with Linux preloaded could choose either, depending on the features they needed and on whether they were looking to the distro or to AMD for integration support.
Thanks for the explanations