The most obvious problem with this plan is that by including GPL-licensed code alongside code under a GPL-incompatible license, you might make it impossible for anyone else to distribute the software. As far as my legal knowledge extend, downstream recipients may only distribute a work that includes your GPL-licensed code if they distribute the overall work as a whole under the terms of the GPL (per GPLv3 sect. 5(c)). You could avoid this problem by employing a GPL exception. Supposing your game was called, say, Foos Versus Bar, you might draft an exception like

Additional permission under GNU GPL version 3 section 7

 

If you modify this Program, or any covered work, by linking or combining it with Foos Versus Bar (or a modified version of that program), containing parts covered by the terms of Foos Versus Bar, the licensors of this Program grant you additional permission to convey the resulting work. Corresponding Source for a non-source form of such a combination shall include the source code for the parts of Foos Versus Bar used as well as that of the covered work.

In this way, downstream distributors have permission to distribute the work notwithstanding the inability to distribute the whole work under GPL terms.

With that problem out of the way, there still remains these problems:

• It isn't perfectly clear that this license allows modification at all (the only permission granted is a vague "use" which doesn't clearly correspond to any particular set of copyright rights). It clearly indicates what you may not do, and requirements for use, but does not make explicit what use is allowed.

• Considering that developers doing internal modifications to files have definitely seen the original code, their code is very likely a derivative of the original code. Per the above issue, this license doesn't clearly license the right to prepare derivatives or, if it is allowed, under what terms they may be prepared. This means the derivative modifications may be disallowed entirety or may have to be made under the original non-commercial terms. If either of those cases applied, then even an all-at-once wholesale rewrite of the entire program could not be licensed under the GPL, unless you applied clean-room practices.

The most obvious problem with this plan is that by including GPL-licensed code alongside code under a GPL-incompatible license, you might make it impossible for anyone else to distribute the software. As far as my legal knowledge extend, downstream recipients may only distribute a work that includes your GPL-licensed code if they distribute the overall work as a whole under the terms of the GPL (per GPLv3 sect. 5(c)). You could avoid this problem by employing a GPL exception. Supposing your game was called, say, Foos Versus Bar, you might draft an exception like

Additional permission under GNU GPL version 3 section 7

If you modify this Program, or any covered work, by linking or combining it with Foos Versus Bar (or a modified version of that program), containing parts covered by the terms of Foos Versus Bar, the licensors of this Program grant you additional permission to convey the resulting work. Corresponding Source for a non-source form of such a combination shall include the source code for the parts of Foos Versus Bar used as well as that of the covered work.

In this way, downstream distributors have permission to distribute the work notwithstanding the inability to distribute the whole work under GPL terms.

With that problem out of the way, there still remains these problems:

• It isn't perfectly clear that this license allows modification at all (the only permission granted is a vague "use" which doesn't clearly correspond to any particular set of copyright rights). It clearly indicates what you may not do, and requirements for use, but does not make explicit what use is allowed.

• Considering that developers doing internal modifications to files have definitely seen the original code, their code is very likely a derivative of the original code. Per the above issue, this license doesn't clearly license the right to prepare derivatives or, if it is allowed, under what terms they may be prepared. This means the derivative modifications may be disallowed entirety or may have to be made under the original non-commercial terms. If either of those cases applied, then even an all-at-once wholesale rewrite of the entire program could not be licensed under the GPL, unless you applied clean-room practices.

The most obvious problem with this plan is that by including GPL-licensed code alongside code under a GPL-incompatible license, you might make it impossible for anyone else to distribute the software. As far as my legal knowledge extend, downstream recipients may only distribute a work that includes your GPL-licensed code if they distribute the overall work as a whole under the terms of the GPL (per GPLv3 sect. 5(c)). You could avoid this problem by employing a GPL exception. Supposing your game was called, say, Foos Versus Bar, you might draft an exception like

Additional permission under GNU GPL version 3 section 7

If you modify this Program, or any covered work, by linking or combining it with Foos Versus Bar (or a modified version of that program), containing parts covered by the terms of Foos Versus Bar, the licensors of this Program grant you additional permission to convey the resulting work. Corresponding Source for a non-source form of such a combination shall include the source code for the parts of Foos Versus Bar used as well as that of the covered work.

In this way, downstream distributors have permission to distribute the work notwithstanding the inability to distribute the whole work under GPL terms.

With that problem out of the way, there still remains the problems:

• It isn't perfectly clear that this license allows modification at all (the only permission granted is a vague "use" which doesn't clearly correspondence to any particular set of copyright rights). It clearly indicates what you may not do, and requirements for use, but does not make explicit what use is allowed.

• Considering that developers doing internal modifications to files have definitely seen the original code, their code is very likely a derivative of the original code. Per the above issue, this license doesn't clearly license the right to prepare derivatives or, if it is allowed, under what terms they may be prepared. This means the derivative modifications may be disallowed entirety or may have to be made under the original non-commercial terms.

The most obvious problem with this plan is that by including GPL-licensed code alongside code under a GPL-incompatible license, you might make it impossible for anyone else to distribute the software. As far as my legal knowledge extend, downstream recipients may only distribute a work that includes your GPL-licensed code if they distribute the overall work as a whole under the terms of the GPL (per GPLv3 sect. 5(c)). You could avoid this problem by employing a GPL exception. Supposing your game was called, say, Foos Versus Bar, you might draft an exception like

Additional permission under GNU GPL version 3 section 7

If you modify this Program, or any covered work, by linking or combining it with Foos Versus Bar (or a modified version of that program), containing parts covered by the terms of Foos Versus Bar, the licensors of this Program grant you additional permission to convey the resulting work. Corresponding Source for a non-source form of such a combination shall include the source code for the parts of Foos Versus Bar used as well as that of the covered work.

In this way, downstream distributors have permission to distribute the work notwithstanding the inability to distribute the whole work under GPL terms.

With that problem out of the way, there still remains these problems:

• It isn't perfectly clear that this license allows modification at all (the only permission granted is a vague "use" which doesn't clearly correspond to any particular set of copyright rights). It clearly indicates what you may not do, and requirements for use, but does not make explicit what use is allowed.

• Considering that developers doing internal modifications to files have definitely seen the original code, their code is very likely a derivative of the original code. Per the above issue, this license doesn't clearly license the right to prepare derivatives or, if it is allowed, under what terms they may be prepared. This means the derivative modifications may be disallowed entirety or may have to be made under the original non-commercial terms. If either of those cases applied, then even an all-at-once wholesale rewrite of the entire program could not be licensed under the GPL, unless you applied clean-room practices.