Facts & Myths:
MYTH: The source code will never be released
FACT: People at both involved companies have displayed interest from a slight interest to a large interest, and this is more than can be said about the majority of PC games. It is obvious that there is interest by individuals to release it, but there is a lack of contact between the involved and a lack of time and ambition. Saying that Epic Games has vowed to never release it is not supported by any statement made at any time ever (afaik).
MYTH: The source code will cost hundreds of thousands of dollars/euros/etc
FACT: The source code would most likely cost nothing. No such thing as the above has ever been said by any genuinely involved individual at any time ever. This would possibly hold true for Jazz Jackrabbit 3, which uses a commercial, expensive, engine (The Unreal Engine) with a license that costs thousands and thousands of euros, but this engine is not used by Jazz Jackrabbit 2. The Jazz Jackrabbit engine is old, and is losing its commercial value quickly. Asking a lot of money for it would just mean it would never get utilised, which is not in the interest of any company.
MYTH: We have to collect money to buy the source code
FACT: This is an irresponsible and useless thing to do until a monetary sum is specified by the involved individuals. Most likely, the source code will cost nothing, and *if* they would ever charge they would not charge in the region that a few hundred usually underage fans could afford (unless it's just costs for the trouble, like lawyer costs, which would be presumptious to collect for right now already) .
MYTH: The source code is of no use
FACT: The community has a history of modding Jazz Jackrabbit 2 through external tools, and lately through editing the JJ2 assembly code. There's been a large amount of tools. Many features that were once considered pipe dreams are now available though
JJ2+. However, access to the original source code would make integrating and adding new features easier, as no reverse engineering would be required and developers would have a better sense of what they can and cannot do on top of the base game. It would also be interesting to be able to look at unfinished or hidden features that are hinted at by e.g. the contents of Anims.j2a; how would the Tweedle boss have worked? Is there anything left of the planned 3D bonus stages? Such content would be interesting if nothing else, and could perhaps be developed into a working feature.
Additionally, as there are very little opensource platformers, having the source would give the community a boost, in that it would attract new people. Currently the wells are pretty dry, but open source applications everywhere attract attention from coders who love to hack away with code.
MYTH: We already have the source code, in the form of decompiled code/editing the compiled files
FACT: The source code contains logic and information that make it exponentially easier to edit the game. There are very interesting things you can do (as shown by Unknownfile's "1.25" project (link)) with just editing the game without the source, but you'll have to set aside a lot of time if you ever want to fix the more complex bugs or - god forbid - add features.