That would remove the point of even having melee units as a shield, wouldn't it? The idea of a shield wall with archers behind them was a common tactic, particularly in Mesopotamian warfare. It would be a shame to lose that. I'm not sure what changing it to a distance of one would really add.
If a mechanics change is needed (I'm not sure it is), I think removing the ability to completely kill through range would make the most sense overall.
Well, just my opinion, but I never liked having to make melee walls anyways. First, I think it messes up the AI in trying to find that perfect spot to put archers such that they can't get mowed down easily. If you buffed their strength - maybe say 30% - they could resist melee attacks better, so it wouldn't be so devastating when they get attacked by a melee unit, which I think could help the AI a bit.
As it is, they already get the benefit of not taking damage on their attack turn because they are ranged. Shortening their range could nerf that advantage somewhat to offer more balance. And I don't see why archers have to be so weak that they necessarily need melee protection, because it's not like archers were completely defenseless historically; usually they would carry short swords/knives for defense. If you compare an archer's strength to a warrior, I think the stats are 5 for the archer but 8 for the warrior. However, the archers actually have better technology, so I would think archers should be a little more on par, maybe 7 instead. And so having more strength would mean they wouldn't need as much protection, which would allows players to use melee more for melee attacks rather than defense so much.
As far as attacking cities, forcing them to be next to the city nerfs an advantage they have over siege units, which is that you can move archers within the 2 tile radius of the city and attack in that turn; whereas siege units have to be set up. By forcing archers to be next to the city, they can't move in and attack immediately, giving the city the attack advantage, and bringing them a bit more on par with siege. But, with better strength, the city attack wouldn't be so devastating and can give you the chance to move them away if they got too damaged, or even launch a volley the next turn and then swap with a melee behind it.
On the other hand, you wouldn't get as much advantage putting archers in your city since they can only attack units next to it. I suppose it somewhat evens out by the fact that the attackers are also limited in range. The city itself can still attack 2 tiles away, just not the archer. May make stationing melee in the city more useful as it give the city more strength. Guess you'll just have to make sure to have reinforcements to take out those damaged attackers trying to get away, since the archers wouldn't be able to reach, right?
Finally, somewhat of a side point, I think it's a bit silly that archers get a range of 2, but as you upgrade them to crossbow, and then Gatling gun, their range then decreases to 1. The 1 tile range seems to work well for Gatling & machine guns, so why not make archers work similarly?
Oh, and I would also add that horses will still have the advantage over archers in this scenario because they can move in, attack, and move out of range again. It probably couldn't kill the archer in one turn anymore, but it would still be a powerful attack. In fact, they probably would be more powerful because you wouldn't be able to camp an archer on a spot that is completely inaccessible to the horse and launch volley after volley on it any more. Best have some spearmen on hand now!