"It... is." replied a slightly disturbed Stirling. " It's a planet stuck in medieval times. No electricity functions on it's surface, thanks to a vehement wizard who, along with many others, saw Imagination Electricity as a dangerous power, not for mortals, or something like that. They didn't agree with it, bottom line. So, this wizard, cast a very powerful spell across the land, that caused Electricity to simply not work, one way or another. The best way it's been explained to me was--and I know this sounds ludicrous-- like invisible energy vampires in the air." -Stirling, To Return Home: Act 1
While Stirling could be considered misinformed and even though it contradicts my opinions, I thought it'd be good to quote the first ever reference to the enchantment. So, we can see that when it was first created (in literary sense), it was considered anti-electrical (which makes sense since it was James's idea). While we may shrug off the limitation to 'just electricity', this still can help us decide on how we will go on this matter, as you will see below.
@Ninjago_Builders: Your ideas are very interesting and they'd be fun to see implemented. Having said that, I strongly disagree.
Firstly, I would like to point out that based on the traditional ideas of the enchantment, Nexus Force Gear of modern and super-modern technology doesn't work in Militiregnum not because it runs on Imagination, but because it uses electricity/is modern and/or super-modern technology. While there might be some doubt over the validity of Stirling's words concerning the enchantment (because he's not an expert), the fact that he packs any Nexus Force Gear instead of none shows that he believes it will work in enchanted Militiregnum. Misguided though he may be concerning how much of technology the term 'electricity' includes, he does not place Imagination in the set of 'things banned from Militiregnum' (that he equates to 'things that use electricity'). So, it's safe enough to conclude that Imagination would work in Militiregnum.
Secondly, Imagination and and Maelstrom are neither technology types nor sources of energy. They are (supernatural) Forces. They are as irrelevant to this conversation as the Force (from Star Wars). While technology and energy sources based on them (which may be discussed) can be built, they in themselves cannot be put into discussion.
Second-and-a-half-ly (not due to a relation between arguments, but because I was too lazy to change the adverbs when I added this), you assume that other planets have been invaded by the Maelstrom, but that is not necessary. It is nowhere stated neither in LU nor in KotOS Lore. Even in the Extended KotOS Universe (including the Stromling Series in it), Elistra was attacked by Maelstrom very much later from the Nexus Corruption, so it's not insane that Militiregnum would not have been invaded, yet.
Thirdly, concerning the Outer Materials idea in general. While it effectively avoids the wishing factor, from a literary point of view, it renders the whole enchantment pointless. James invented the enchantment's idea as a way to explain why Militiregnum is stuck in medieval times. While its necessity on that front may be doubted, it is certain that it serves no other purpose (at least it did not at first). It would have served the purpose of spicing things up, but for the fact that James negated its existence mere paragraphs after inventing it. If internal materials could be used for the development of technology, though, then the enchantment would not be able to prevent it, thus beating the point.
Fourthly, as you might be thinking that it can serve different purposes now, because ever since then the enchantment has been modified to still survive, even if in a weaker form. However, the greatest use we could find for it -Dewin reinforcing the enchantment for a period of time to make technology malfunction again during the final battle of SA- would be rendered unusable. Fifteen years in Militiregnum, thedude would have gotten to build new technology with local resources, thus making it immune to the enchantment.
Fifthly, the idea of the Materials absolutely contradicts everything that has been said as of yet about the curse. While the anti-development idea can be explained with reasonable arguments that do not render anything non-canon (the Militiregnum people's misinformation of what is electricity and what isn't), the anti-foreign-material idea is not compatible with phrases like 'anti-electricity enchantment' and 'anti-technology enchantment', since the latter ban electricity and technology respectively originating from Militiregnum as well.
Sixthly and returning back to Imagination and Maelstrom in particular (because this argument concerns my LU philosophy and could be considered invalid I write it last), Imagination and Chaos are not foreign to Militiregnum. They are Forces that exist in the whole Universe. While the Nexus is in Crux that doesn't mean Imagination does not exist in the rest of the Universe. Think about it, every minifigure has the power of imagination and I don't think imagination with capital I and lowercase i should be considered as entirely separate things. Does not every minifigure have a Creative Spark? Even considering basic LU only, it is stated that one unlocks their Imagination, not acquire it. That means they already possess Imagination; it's just not accessible to them earlier to its unlocking. For symmetric reasons, it could be argued that the same applies for Chaos.
Phew, I'm done. I'm also late! Why N_B? Why? :P