The Cocoa Cola reference doesn't apply, they are producing the product, and selling the product, without publishing the recipe. It's the recipe that is a trade secret, and not the product itself.
As for reverse engineering being considered a legal means of acquisition, are you basing that off the Wiki? That's the first place I found that referenced it (though I did find it in other places as well.) First, reverse engineering is never listed in the actual code itself. The only places it is located is in commentaries of the code. Second, in the places I found it, I found it in 2 forms. The first just listing "reverse engineering" as acceptable, the other listing "reverse engineering, unless prohibited" as acceptable. Reverse engineering of a trade secret is a risky proposition. In these cases, it's left up to a court to decide (on a case by case basis,) whether reverse engineering of a trade secret is or is not legal. On digging out my text book (took a while, I'm just glad I had it here,) and re-reading the code in detail, I did, however, come across a stumbling block that you didn't bring up. A trade secret does lose its protection if it is no longer profitable. The only issue with that is, that it is still up to a court to decide, and is not arbitrary.
If you want something more specific to reverse engineering protections, why is there not an exact duplicate of Cocoa Cola available? Or Pepsi for that matter. They are still the top sellers of cola drinks, and yet they are still singular (for over 20 years, so patent doesn't apply.) A detailed chemical analysis, and some trial and error maybe, could give any company that wants to try everything they need to produce an identical product. Yet it hasn't been done. Maybe it would cost the same to produce, maybe they could find a way to make it cheaper (outsourcing production maybe.) But still, nobody has done it, even if to just give themselves an "in" to a market that is mostly exclusive. To remain with your Cocoa Cola reference 😀
The key here is that, yes, Grand Island Cola (made up company, apologies to you if you really exist,) could analyze and reproduce exact replica's of Pepsi & Coke, then release them as their own products (they obtained the recipes through acceptable means, right?) But they would then be immediately taken to court over the issue by one or both of the other companies (Coke & Pepsi.) They would spend huge amounts of money in court defending their "legal" acquisition. Coke & Pepsi have a financial stake to protect the recipes, and even if they lose it's still worth the attempt (they get to paint Grand Island Cola as a thief in public opinion.) If they win, the maintain their exclusive product. Meanwhile, Grand Island Cola is facing bad publicity, the possibility of losing in court and facing punitive damages, just to maybe gain "equal" footing.
In my class notes, it was commented by the instructor, that the key to trade secret protection is taking steps to maintain the secret. Putting a seal on a piece of hardware denying the end user permission to open it up is all that is necessary. Covering a key screw, putting a sticker across a seam, etc... These were specifically mentioned. Also, just putting a line in the manual stating that opening up the product isn't allowed, was sufficient, but you then had to ensure that sales of a used product always included the manual. Extrapolating for software, putting a notice in the software somewhere, even if it isn't easily seen (tiny print,) just seen at least once (during installation maybe,) is sufficient. The steps didn't have to be effective, they just had to be present.
The point is moot though. If the DOSBox authors want to take the safe course, that is their prerogative. If they want to take a chance, knowing that there are 2 avenues of defense and are not likely to face the issue anyways, that is again their choice. My main question is, as long as they can come up with their own format, or use one that is completely open source, why take any chances at all? They are under no obligation to make things extra easy for us. There are also plenty of end users more than willing to create converters for favored formats. The only thing I'm going to ask for is "something", "anything" to let me play my games again 😀