Can't switch weapons in tactical, a far as I know.  

Oh! Is that an oversight? Something that will be patched soon? Or WAD? Seems very odd to me. If I can't switch weapons to melee, there isn't much point in carrying them around.

Also, if I cannot switch weapons, then it seems that melee abilities such as "sweep" should be disabled if no melee weapon is equipped or equippable.

I believe it stands for 'Working As Designed'. Not positive, but it makes sense in this context.

As far as the knife usage goes, you might need to check the Skills menu, not just the skill and spell bar (button that says 'skills', located beneath the skill and spell bar and next to the button that says 'spells').

If you were so inclined, you might be able to mod in something that would 'correct' this oversight - perhaps changing ranged weapons to a special ability weapon similar to knives and using them to give a special attack, or doing the same for some kind(s) of melee weapon. I have no idea how this would impact the ability of the AI to use such weapons, though, so it could greatly reduce the effectiveness of AI archers if you were to do this.

Judging from the way bandits use throwing knives, while they do prioritize using that attack over using normal melee attacks, changing bows to a special attack weapon and giving it a cooldown would cause the AI to have their units continually close the range, which negates the advantage they should be getting from using a bow in the first place. I suspect that you could instead include an initiative penalty on the bow, or cause the use of the bow to cost an extra turn, and that would allow the AI to make use of the bows without constantly closing the range (I think).

Another possible issue, if you make bows a special attack with a range limitation, is that the AI will first close to within proper usage range, and then end their turn, and then on their next turn make use of the special attack, at least judging from how bandits use throwing knives.

You would also not really have a distinct archer model, if you turn bows into a special attack option, as I don't think that any accessory affects the unit model, although I suppose you could go for making a secondary weapon slot that provides some change to the model.

Having the cooldown also might not directly relate to the current relative strengths of bows, since the number of turns that you 'lose' by using a bow rather than a melee weapon varies by the total initiative of the unit.

I agree that tough choices are good, but that in the case of Champion weaponry, this is not one of them. The main reason is this: We already have in place a system of upgrades upon leveling that each Champion may invest in; these involve choices. Normally, one might go down the path that most RPG fans know: minimaxing your advantages and specialize. That is, a Champion who wants to wield a bow will probably not want to invest in special melee damage bonuses, and vice versa. Yet, one could imagine the situation in which a player wants one of his Champions to be less good in both  melee and archery, but be able to do both with some modicum of success. The system we already have allows this -- except for the combat UI. c-RPG players are used to weapon swapping and alternate sets. I think it would make sense to enable it in the UI.

Yes, it should cost the traditional "action point" penalty. Wielding both a bow and a sword simultaneously is a bit ridiculous even for fantasy.

Yes, actually, I like to roleplay my champions a bit and prefer to arm them accordingly and flexibly. In some situations, I want to be primarily ranged, in others, melee. Using a bow in melee range just feels wrong. I have no problem with an initiative penalty for switching weapons.

I think you make a valid point Onomastikon, but I still prefer the current system. If the champions could wield both a melee weapon and a ranged weapon it would be a no-brainer, every champion would have both, since it's such an obvious advantage. I like the fact that I have to choose.

you didn't know

Nah, you can't because the devs chose it to be so, for whatever reason, I don't mind omastikon (Did I spell it right? ) asking and/or discussing the subject, but I just state my personal ideas around the subject:

If you could switch weapons during combat, weapons that counter specific creatures/enemies becomes much more valuable and much easier to use, and it would be yet another benefit to high combat speed (move out of attack distance, switch to whatever weapon, go back into the fight). So besides man-hours spent on either neglecting the AI, or teaching the AI using the system, I think its better left where it currently is which worked fine for me.
Note: That was my point of view

Sincerely
~ Kongdej