If the source for the SDK is available, what part of PhysX isn't available? All of their core algorithms and solvers are available, although the Flex source code isn't available.
Game works is another kettle of fish thigh.
Not all solvers are available, GPU solver's aren't, FLEX and APEX are also currently not available.
FLEX source won't be released as far as i can tell APEX will be released in some form or another in the future.
The basic CPU solvers are there, but the license doesn't really allows you to modify them anyhow.