Is weapon length taken into account in combat, and if not, will it ever be? It is my understanding that the spear is by far the most popular weapon in the history of warfare. Now, the spear has a lot of things going for it. It's cheaper, easier to make, and easier to use when compared to something like a sword, but I think a HUGE part of the spear, and pole-arms in general, is the ability to stab the other person with your pointy bit of metal while keeping your soft and squishy body as far away from their pointy bits as possible. But in my experience, when I move into a tile adjacent to a goblin thief, he will be able to take off my ear with his nine inch dagger before I get a chance to stab him with my twelve-foot pike.
The problem is that spears are typically one-handed spears in this game. Those would really be used more for stabbing around a large shield from the same sort of range you'd be using a sword, anyway. (Which is, incidentally, exactly how they are used in this game.) Spears were incredibly common throughout history, but spears and lances and polearms are all different weapons that don't have interchangable lengths.
The sort of polearms, like pikes, that really were for holding enemies off at a range of 12 feet or more were often so heavy and bulky that they would be essentially impossible to use in non-formation combat, where the enemy could just sidestep your pole and attack from the side faster than you could turn. In fact, most soldiers who carried polearms of the sort that keep enemies at bay beyond normal sword reach actually carried shortswords at their sides and simply dropped their pikes as useless when it came to actual melee.
Beyond that, there's also the whole fact that the game still does not have hard definitions on the size of its tiles (although I do believe 10 feet is a reasonable guess), and 20-ton whales fill the same space in this game as do butterflies. Technically, even reaching into the next tile, though, should take a nearly 10-foot reach, even assuming 10 foot tiles, since you have to reach out of your own tile and into theirs.
My understanding regarding length is that it is figured in when determining how deeply a blow my go - you may not stab a weapon deeper into a fellow than the length of its blade. To my knowledge, it is not possible to exceed this by additionally plunging one's arm into the target's body, but if it is, this nonetheless happens after the entirety of the weapon has been dealt with.
I actually see this as a bit of a weakness of the system Toady has set up, as it appears as though the game only calculates the weight and length of the weapon when dealing damage. This causes problems like, if I was punching someone, and dealing serious damage to them, but then stop and pick up a tooth, and then punch someone with a tooth in my hand, then my punch suddenly becomes based upon the stats of the tooth, and becomes completely harmless as an attack. The weight of the rest of the arm behind that attack is completely meaningless.
Being able to put the momentum of your body into a thrust, as well as being able to just plain punch through tissue if you really are that strong, should be incorporated into the way that combat mechanics works. (Although granted, this was from experimentation back in 31.01 and 31.03, so it may have changed by now, even though I don't recall seeing anything to that effect.)