When I said I wanted to talk about the other ideas mentioned in this thread I should have known that you would jump right to the suing bit
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I am no lawyer but I am pretty versed in software distribution licenses. So let me expose my point of view on this as if I were an outsider.
First, there is the code. That has clearly no connection to DF and there are laws in place to protect me from exposing my code created for the situation when some money grabbing entity tries to profit from it. You and I know that this is not the case here, but those laws are in place.
Then there is the general idea. I think that when talking about the general idea the conclusion is the following: another game in the same genre. Other verdict would be disastrous and set a very dangerous precedent for the entire open source movement. While I am not open source right now but considering it, almost all open source is about reproducing someone's closed source idea. If you enjoy using Linux for example, there is a good chance that your favorite application is a clone of a Windows or Apple product. Linux has been fearing unreasonable patent laws for years and there was a moment when you could cut the FUD (fear-uncertainty-doubt) with a kitchen knife. Some distributions make a point to only include packages that are as safe as possible form a patent/IP point of view, giving you a fairly useless operation system for the masses unless you plan to do a console based server, where Linux shines and is the best and safest bet. And some of you may argue that the difference here is that they are recreating something and giving it away for free. Make it about higher morals. But this is a legal system we are talking about and the moral issue has been solutioned already: if you distribute something protected you are eligible to face punishment if you charge money or not. Otherwise, claiming that morality allowed you to break some rules makes you judge, jury and executioner and we all know how well that works generally.
Then there is the specific content. The tiny parts, like blade weed (to much plump helmet talk already; I am sure that somewhere somehow all plump helmets have a serious case of the hiccups). No instance will accept a case based only on a few glimpses from a blog, especially when it can be proven that historically at the same moment there were claims that these were only for testing and demo purposes. Basically, it falls into the "mock-up" category. Name your favorite software package (besides DF) and imagine that you are a developer with an idea and would like that idea put in action based on the above mentioned software. To make it more specific, let us take a shooter and the idea being a new rendering mode based on ray tracing. And to mock-up this rendering engine, you hacked a commercially available shooter. The assets are still there, so is the engine, but you replaced a couple of dlls. Talked about it in a blog. Made a few demo videos. Have intention to sell a product based on the new rendering engine with the new ray tracing algorithm, but with no connection to the commercial shooter. Your idea works with any shooter and you are not dependent on the original product. You only used that to show that you can. Now, there are tons of people out there doing that to varying extent. Sue away. Sure, in some cases the specific person may have invalidated the EULA (end user license agreement) by tinkering with a product, but that won't get you that far. Take Apple for example. The legal battle is done and people rejoiced. You are now legally permitted to jailbreak your iPhone which you bought and own to allow legal software on it that Apple doesn't want there. So Apple can no longer say: "You can use only our Internet browser, no other company is allowed to create a fresh browser for our machine and you are not allowed to buy or install it.". You may loose warranty, but it is legal, i.e. you will not have any legal troubles. Of course, this varies from country to county, which leads me to my next point.
The reality. And the reality is that IP/copyright laws are by no means universal. There are countries out there, where you go to a supermarket, to the music store and every single music CD has been burned in the back office of that store on a cheap computer. The case is of low quality, scratched often and the label is printed black and white in the best case scenario and just a piece of paper from a notebook with the album and artist name misspelled with a pen in the worst case scenario. Or even cassette tapes. These shops are legal there and they pay taxes. Countries, where this is the norm and nobody cares about copyright law and even less about paying royalties. Where you have no broadband Internet to illegally download music so you buy it for dirt cheap from a shop and you are happy. And the entire musical industry with all its money has nothing that it can do about it. Nor do all major copyright international movements. Thing are progressing in those countries and laws are "catching up" to international standards slowly, but keep in mind if such a copyright law is given today, it may take a couple of decades before piracy goes from the major form of distribution and the norm that people are used to a small part of the population so the law can be considered a success. In such countries after a year or two, politicians will appear on TV, complain loudly about how much the campaign the "educate people's sensitivities" has cost them, money taken from other crucial domains, because of evil international pressure, and how piracy has gone down 3%.