Here's my OpenSim running,
I'm now going to try to populate it with accessible contents. This could be an easy way to prototype a framework, set of standards, or test environment in which we could let blind people interact with one another.
Unfortunately at present script support in OpenSim is extremely limited, so audio playback is not possible.
The only current way to create such a test environment will be by renting use of Linden's commercial servers.