While in a decently designed engine based on decently designed software, a single dimension such as length on trails would be easy to code, I suspect it would cause significant amounts of lag. In addition to this, I don't think weapons actually have any measurement of their length encoded into them.
Doomknight V1 would provide an easy win button for the challenges; the spoils of which, I might add, are completely unnecessary for someone with V1 for any purpose, given how powerful the class is. There's also the issue that, if you have Doomknight V1, the rewards you might earn by using challenging strategies are simply slower and less advantageous to using V1, making it a penalty for playing the challenges as they are designed to be played. Of course, one might argue that it makes no difference what's available, since the experience of playing is the same... but this logic means that any aspect of the framework of a game is irrelevant provided you can do the same things in it.
For example, if you could give yourself any amount of gold in-game within a minute, you could theoretically still farm for gold. But that would be time wasted. Essentially, games that just give every reward immediately with no progression or structure are not enjoyable for most players, since the rewards bypass the gameplay.
In the same way, at least one member of this discussion has bypassed the gameplay using V1, and apparently doesn't understand the gameplay mechanics beyond life carving and nuking.
Reminder that many discussions about Doomknight (particularly V1) are unlisted banned topics on the forums, for the same reasons as we've seen in this thread; it's commonly brought up by inexperienced players, and frequently leads to arguments.
There are quite a number of players who self-challenge (Baron used to, though he's on hiatus, Erosion has his chickencow strategies, TFS does everything in every possible combination in every possible way except at low levels, I do low level DA and annoy TFS, etc.). But in terms of the challenge rewards, there is a minimum bar, and for the most part that bar is having a decent understanding of how the game works.