Shield Bash turned into an AOE attack.

[Ralvenom]

As was said we do have Spirits within already for silence.

I dunno maybe it'd be better to just allow paladin to cross class overpower? I'm not sure how that would be balance wise. But it'd do basically the same as what you're asking minus the AoE spell interrupt which isn't really needed.

A more elegant solution would be to add a small damage component to Flash. Let's examine Overpower & Unleash, in comparison to Flash.

Overpower:

Delivers an attack with a potency of 120 to all enemies in a cone before you.
Additional Effect: Increased enmity

Unleash:

Deals unaspected damage with a potency of 100 to all nearby enemies.
Additional Effect: Increased enmity

Flash:

Increases Enmity in all nearby enemies.
Additional Effect: Blind.

If a 110 Potency amount was added to Flash (for PLD only, via a trait), that would really solve PLD AoE issues.