I would rather have Shattered Retreats be changed in the following ways, rather then remove them entirely;
- Forts stop shattered retreats. I'm not suggesting this because that's how it works in EU4, but rather because it makes the most sense. A fort, being a sign of active low-level military presence, would likely force a fleeing army to halt. It's not perfect, but shattered retreats are awful anyway, so this would probably have to be the best workaround.
- If a Shattered Retreat moves into a province with a enemy army in it, then battle occurs normally. IE: A retreating army shouldn't be able to somehow avoid a secondary army waiting for it to flee from the battlefield. Cutting off a fleeing enemy that attempts to retreat across a river and get promptly slaughtered should be a thing.
- If the leading commander of a hostile nation has the proper leader trait, then his army could interact with the shattered army as normal. This could allow for, say, a commander with the Rough Terrain Leader trait to track down and interfere with a army fleeing through a hilly or forested area.
- 'Unlanded' rebels that are hostile to all, such as peasant revolts, attack shattered armies as normal. Giving that 'shattered' armies are disorganized messes, other disorganized messes could be able to fight them. In larger realms in civil wars, this could allow for such sights as a band of religious fanatics tearing apart the fleeing armies of a rebellious duke. Mobs should be able to deal with mobs, basically.