for me opensource support for the 7970 is different to your "Imagination" of support.
there are proved support because there are valid code commits in the kernel.
support=people work on it.
means a true way.
the oposite of support is fglrx=they claim they are "finish" with the implementation and push a release but the release is FGLRX style '''''''business as usual'''''' means 'shit as usual'
this is the oposite of support because you will never get a working driver ! NEVER!
i fight against catalyst/fglrx bugs for years and every bugfix in a new release broke another part.
you can prove this with an technical argument: can you do a git-bisect regression testing with the catalyst? NO! this means bugreports are USELESS!
do you prever lies like the fglrx or the trueness? i prever the trueness of the radeon opensource driver with git-bisect regression testing.
"3) Bridgeman has commented he never sees opensource driver to be used on mid/high end cards"
i do have a different point of view: you need highend class hardware for the opensource driver.
for example you need a faster cpu and faster gpu and you need higher PCIe standart PCIE3 for example-
because tests shows that PCIe standart upgrade to have a higher impact on opensource drivers than on the catalyst and the opensource driver is also more bottle neckt by the cpu and you need a faster gpu card for the same result.
but in the end you get the same result and this is the only part.
Opensource is the MONEY WORTH!