Tons of things write about this but my real life schedule has cratered quite a lot the last days so I got to restrain my self a bit (which I failed to apparently, below follows a novel or such).
It is my strong belief that the ultimate driving force behind individual design decision in Spring, Spring mods and other similar game projects (like Freeciv or the Sauerbraten Engine or mods to Battlefield 2 etc) is such a
trivial thing as personal PREFERENCES of the persons making those decisions. Often those preferences are disguised as "the only technically possible way to do/design things" or similar bullsh... er... utter nonsense (not seldom is this used in a slightly modified way to create the ultimate insult to a person who makes a feature suggestion: "you don't want what you suggest but you don't understand that" to make them seem sooo stupid and naive that they are unable to understand what they want themselves).
Sometimes design decisions really are technical in nature, sometimes people request features which have dramatic implications which makes those suggestions problematic even for the suggester BUT the cases when those things happens and there aren't just a matter of personal preferences vs personal preferences are RARE.
And the bitter truth is, dignifying preferences are never justified. They are just preferences.
But there is a BIG "BUT" here... and that is, even if coders and content creators base their decisions on such a trivial thing as their own personal preferences (instead of some higher wisdom etc) THEY GOT ALL RIGHT TO LET SUCH A TRIVIAL THING DRIVE THE DECISIONS.
Actually, in volountary work, nothing else than preferences really should be the basis for design decisions. Sure, one has to get along with others in the project (meaning both contributors as well as product consumers) and make some tradeoff regarding what preferences should prevail in the work on the project and what preferences should be deferred but basically, if a volountary contributor find that he has to work completely against his preferences, he/she will go do something else.
Being able to contribute according to (at least some of) one's preferences is key to keep up the motivation to contribute. No motivation, and one works with something else.
The use of GPL or other open source licenses are at the end of the day something that is based on the content creators personal preferences. He is not required to do anything other than what he feels like in this respect. Taking away the volountary part of the GPL and other open source licenses defeats a LOT of their power, IMHO. Sure, they contains a number of restrictions, but those restrictions are never FORCED on anyone, there were always some point in time before when one does a volountary decision that lead to those restrictions being applicable. E.g, it is a volountary act to decide to use GPL or not as a license for one's project. It is a volountary act to start making changes to a software one should KNOW is GPL and thus be subject to the restriction that one HAS to provide the source of those changes.
NEVER EVER meddle with the actual meaning of the word "volountary". Never over and over again tell someone that they volountarily shoud do something, because if you do and they do what you suggest, the are barely doing it volountarely, rather, they are coerced to it, defeating the "volountary" part of it.
Then I question the viral nature of the GPL. If I design a model for a Leopard tank (a modern German tank IRL BTW) and release it under GPL and Centipede use that model in Operation Polaris, that does not implicitly turn Operation Polaris GPL, I just cannot believe that. What happens is that Centipede is not legally allowed to forbid other ppl to take that specific Leopard model out of the Operation Polaris mod and use it. However, the remaining IP of Operation Polaris is still not forced to be GPL. Sure, I'mn not an FOSS lawyer, but from a common sense perspective.
Regarding opening up a project or not: by keeping a project "closed" under a "ask the author" sort of license (formal or informal), the creator do create a barrier for others who wish to contribute. This is both good and bad, and that barrier is not necessarily put there on sheer bloody mindedness or asocial destructivity, but it is put there as a measurement of creative integrity and to maintaing some control of one's dear project. Why should one want to control one's project? Well, you might for instance want to avoid that the project is hijacked by ppl who has dramatically different preferences that you has. I personally would be very distressed to see that mod/game/whatever with an intended wargame focus becomes "hijacked" by a bunch of contributors who all are more bent on creating a game with a e-sport focus: suddenly the project is heading in a direction where a lot of features I would like to see implemented are ignored or even considered "dangerous" (as they would be in the way of e-sporting). On the other hand, I might be willing to take the risk in order to get manpower to the project (hah, as if anyone would appear, when everyone got their own projects instead

) and thus release it as GPL. Or, maybe I'm keen on seeing parts of my project (like said Leopard tank) live on in other projects and using a license where I don't enforce my explicit permission makes it easier for others to use my work, especially for trivial things like just playing around with it on a more casual basis to see if is useful.
But Smoth is right, if someone release stuff on a closed "ask the author" permission but then it turns out that the author always says "yes" to any request to use his/her content, then the software is pretty much open, isn't it?
Agh, that was quite some text anyway. Hope noone was put to sleep.
Maybe we should continue to discuss Operation Polaris itself in this thread? I just asked for the license to determine how to contribute/use the Operation Polaris content (that is, with focus on OPERATION POLARIS side of things, not with focus on the LICENSE side of things...).
Otherwise, this discussion is doing fairly Ok, but I would love to some people try to calm down a bit before they write their responses. Some tone in here is getting a bit... well... out of hand.