I think this is a UI issue too.

There would have to be an acceptably convenient way to access other weapons mid combat that didn't make switching a complete chore, because otherwise no one would do it and it would be a waste of effort.

There also may need to be code changes to the way weapons and combat work together.

Lastly, as you've already suggested, there could be balance issues. Bows aren't a huge conern of mine. What about weapons that improve initiative or give a bonus that's particularly useful early in a fight?

Really, right now there's not much of a reason to change weapons on the fly other than switching from ranged to melee. Weapons don't act differently under different circumstances, and one will always be dominatingly better than others. If this changes I support going through the work of implementing this entirely new system into the game.

As it stands, I don't think it's worth the effort.

Fair points. I don't know for sure if ranged works exactly the same when you are standing beside the enemy but my impression was that it did. In any case I guess you can usually step back.

Ideally units holding ranged weapons should be more vulnerable to melee than if they had a melee weapon out. Shields partially implement this but holding a two handed weapon is no better than holding a bow which seems a bit wrong.

Anyway back to my suggestion. There are two reasons I made my suggestion:

1. It would be more realistic, real life archers usually had backup weapons for melee combat. I like the idea of my hero firing off a few shots then when the enemy get closer dropping the bow and charging into the fray with his sword and shield (or whatever).

2. It would allow my heroes/sovereigns to use bows but still get some use out of their melee weapons and shields (and vice versa).

I remember using kiting a lot with my ranged heroes in MOM.  This was pretty unrealistic  but was partially balanced by the fact that enemy units could corner me against one of the edges of the map and that if I moved, I could only get one shot off (instead of two if I stayed stationary).

I'm still vacillating on this, tbh.  I probably wouldn't mind seeing the ability to swap weapons be put in there, if counter attacking was also brought back and penalties added to an archer trying to use a bow while being attacked at melee range.

Perhaps combat could work like this:

1]  Any unit can perform any combination of two combat functions during their initiative round: 

   a] make one melee or ranged attack

   b] move up to half its movement/speed allowance

   c]  make a block/parry action that increases defense against the next attack targeting it

   d]  swap weapons

2]  If a defending unit is attacked by melee (only!) it gets one free combat action immediately after the first attack.  It only gets one of these in between each of its own initiative rounds and if it chooses to attack as its action (instead of move, defend, or swap), it may only attack the unit that attacked it first.

3]  Ranged combat has a penalty to hit at long range, and is impossible to perform while an archer is in an enemy's zone of control.  (edited).

3b] All ranged weapons have limited shots per combat.

4] Zone of control is still a factor and limits any unit moving from one hostile zone of control into another to only one space at a time

This isn't a perfect system but it might preserve balance while restoring a little more realism.  No idea though on how hard it might be to completely revamp the current tactical system we have now..