Sadly it's very unlikely to see a source release - Doom is the exception rather than the rule as John Carmack pushed for open-source releases of all of the engines that he developed at id Software.
Going freeware is even less likely as not even Doom is freeware, GTA1 and 2 are the only examples I can think of, and they're no longer available anyway.
The problem with a source release too is that there would be no legitimate way to make any use of it - the compilers used are part of confidential Sony SDKs, it would be impossible to boot a recompiled disc on an unmodified console, and private sale of development hardware that could run it is not allowed either.