Yes, I know and understand that rule 4 exist to prevent the server turning into creative mode where scarcity doesn't exist. However, I believe that TNT duping, as similar as it may sound to other duplication glitches, should be allowed on the server.

First and foremost, it does not actually duplicate resources. It "duplicates" TNT by creating a primed TNT entity without consuming the block. As you are unable to un-prime TNT, you cannot actually generate TNT items from this. This method cannot be applied to valuables, such as shulker boxes, as it is specific to TNT, so it wouldn't break the economy. Also, this does not duplicate items nor blocks, so the chance of getting slippery slope arguments for resource dupes is minimal.

Secondly, it is a very useful mechanic. The use of TNT duping in technical Minecraft commuities is widespread in lots of creations, such as tree farms or world eaters, which would otherwise be infeasible or impossible without TNT dupers. While wither cages exist, they often require breaking bedrock (which is an unintended bug), and bedrockless/movable cages are often unreliable, potentially releasing a wither into the wild, causing massive damage to the world. Aren't we supposed to make technical wonders in Cemetech?

Last but not least, it is officially acknowledged as a game mechanic. As you can see in https://www.reddit.com/r/Minecraft/comments/fkt9jf/comment/fkv33q3/, slicedlime, Minecraft's Java Tech Lead, acknowledges that this mechanic is intentionally left into the game, just like quasi-connectivity (which also started out as a bug and later accepted as a part of the game). Therefore, it's not just an unintended exploit.

You may ask, "wouldn't TNT dupers allow griefers to easily destroy large bases with ease?" Even though it has major destructive potential, it's not an easy way to grief, as they require lots of slime blocks and dead coral fans. Slime blocks are difficult to acquire in large amounts without a farm in a slime chunk (which is a big undertaking in and of itself), and dead coral fans require a silk touch pickaxe to get. So, it is not a big issue for potential abuse.

In conclusion, the benefits of allowing TNT duplication massively outweighs the disadvantages of allowing it, therefore I propose that it shall be placed under an exception to rule 4.

Comments are welcome.

To add: there are multiple ways that TNT duping can be used.

The most obvious one would be tree farms and cobblestone farms. Wither cages also work for them, but obviously a TNT dupers will be much safer in case of a failure. Also, the server is run on paper, and paper is known for breaking many technical builds such as some wither cages (unlike fabric).

Also, tunnel bores would be much more feasible. Wither based tunnel bores are unstable, even in vanilla, so it's a fool's errand to make a wither tunnel bore on paper. Therefore, TNT duping would greatly simplify tunnel bores, and also increase its safety.

Last but not least, world eaters. They can remove extremely large amount of blocks and create perimeters easily, and they avoid the huge mindless labor of digging out chunks manually. Also, by removing caves near farms, they can reduce unintended mob spawns, improving the performance of the server, as it does not need to simulate mobs that no one would see.

All good points, and honestly I hardly see any reason not to allow it. The only argument I can possibly see against it is that some admins might prefer people work to acquire/craft a bunch of tnt instead.

On the other hand, it is a mechanic intentionally left in the game, as you said. Plus, Kerm has already built some tnt dupers on the server just recently... so I say it should just be enabled in the configuration file.

I am actually in favor of this. I'm very firmly against duping of items, as we are a survival server where we do want impressive survival builds, a very different class of experience from building something impressive in creative. However, as someone who loves to automate as many farms as possible, if TNT duping is an "intended" behavior, I'm generally okay with allowing it. Minecraft has never tried to be realistic about limitation of resources: I just build moss farms, for example, that use moss plus stone generated by water + lava to generate moss, turning it into bonemeal, which generates more moss and bonemeal with more infinite stone, ad infinitum. Growing endless crops without depleting plants or soil is the norm, water sources are infinite, etc. My biggest concerns would be (1) griefing - I want to soon get Towny set so people can protect their builds without any cost, especially with our new whitelisting, and (2) duping other items - I thought I've seen that TNT dupers can dupe rails too, but I'm not aware of other items being dupable with them.

I'd be on board with allowing TNT duplication, but I believe that can create a slippery slope of "well you allowed us to duplicate TNT so why not diamond blocks?" It is important if this becomes a thing to quantify that it has been allowed because Mojang's developers have indicated they left it in deliberately and it has advanced from bug to "feature", and thereby differs from other duplication glitches that remain, for now, bugs.

I personally think that the only condition for this should be "does it make the game more interesting?"
Allowing general item duping usually does not make the game more interesting, as although it is mildly interesting to design and build an item duplicator, at the same time it makes a ton of interesting gameplay completely irrelevant.

TNT duplicating definitely falls into the "more interesting" category. It makes a large number of contraptions that were previously infeasible feasible, like cost-effective automated farms for relatively low-value items like wood or cobble, and even some things that were completely impossible, like movable TNT mining machines. These types of builds have a huge amount of depth to them, and are extremely interesting to many players, especially those in Cemetech's audience.
They do also make some things somewhat irrelevant, but I would argue that these are largely tedious tasks that aren't really interesting at large scales, like mining sand and crafting TNT. The biggest thing would probably be gunpowder farms - you have much less of a use for those if the demand for TNT is reduced. However, they're still not completely out of the picture as the result of allowing TNT duping - you still need gunpowder for rockets, after all.

There is also the added complication of multiplayer - you not only have to consider what's interesting for you, but also for other players. Even if I were to find duping certain items to be more interesting, it might make your experience feel less rewarding knowing that I was able to get the same thing for less work. TNT duping is in my opinion unlikely to do this, since just duping TNT on its own isn't very useful - you still have to put in the effort to build a contraption that uses it, so it doesn't devalue someone else's work in the same way that general item duping does.

There are a few more things that I feel like this argument could be extended to - for example, duping certain highly non-renewable items like dragon eggs, large ferns, tall grass, elder guardians, and items intended to be unobtainable in survival.
In singleplayer I would add elytra to that list after the End is thoroughly explored, but recognize that that might make the game less rewarding for other players in multiplayer. But that's what ender-dragon-dropping-elytra datapacks are for.

Yes, Towny would be a great addition. Even though it's technically the same bug that allows TNT dupe and carpet/rail dupe, they require a different setup, so it would be obvious at a glance. Besides, it's already a bannable offense to dupe carpets/rails (which are not items of very high value), so it's unlikely anyone would dupe carpets or rails.