dnd 5th – How would the game be unbalanced if the removal of the limitation "requires a free hand" for crossbows?

I work on statistics for the royal guards of a homebrew capital – using the captain of the guard as a model. I gave them a crossbow and the gift of the crossbow, thinking that it would allow them to hold a shield in one hand and a crossbow in the other.

Expert Crossbow mentions on PHB p. 165:

You do not know the quality of the crossbows with which you are competent.

• Being within 5 feet of a hostile creature does not disadvantage ranged attack rolls.

• When you use the attack action and attack with a one-handed weapon, you can use a bonus action to attack with a crossbow that you are holding.

At first, I thought it would be enough to wear a shield to attack with a crossbow, but the Loading the property actually says:

Due to the time required to load this weapon, you can only use one piece of ammo when you use an action, bonus action or reaction to shoot it, regardless of the number of attacks that you can normally do it.

So, "loading" refers to the loading speed, and the feat makes you faster. This is the Ammunition Property which, by RAW (PHB p.146), does not allow to wield a shield when attacking and reloading a handbowbow:

[…] Firing ammunition from a quiver, crate or other container is part of the attack (you need a free hand to load a one-handed weapon). […]

Related:

In what way does the imbalance of the game with the suppression of the limitation "requires a free hand" for the crossbows? From a thematic point of view, that makes sense, because in my context, this city is rich enough to have a technology as sophisticated as "semi-automatic" crossbows (although it may work). Since my gaming environment allows it, it would be fair that it would also be an option for the PCs – if they acquire such a weapon and / or such training. I am mostly interested in the combination shield and crossbow in hand, but if I ignore other potential exploits that would unbalance the game, please inform me.

I can allow this for NPCs (for my guards) because I can simply calculate the new CR, based on an increase in DPR and AC. As a DM, I have enough control to keep this balanced at the table. When you allow it for PCs as well, I am not sure of the unhinged exploits I could neglect. A good answer includes an analysis of the mechanical costs and benefits for personal computers when eliminating the limitation "requires a free hand to charge".

To remove this limitation, I think of three possible ways:

  1. Modification of the Munitions property of hand crossbows in particular.
  2. Add a feature to the exploit of Crossbow Expert.
  3. Solve it by magic by making the sophisticated crossbows of the Royal Guard, unusual magic weapons that can be reloaded without having your hands free.

An amazing answer includes a balance of games analysis on these possible solutions.