Two dices collides differently than planets do.
For one, they are not spherical. For another the energy released (during small collisions) is not enough to visible deform or fragment or melt the dices.
Since planetary collisions are the prime focus right now, that is where we put our effort.
The previous version of US used a third party rigid body collision system which was used throughout. That meant that dices looked right and planets certainly did not.
However... we will be adding support for smaller scale collisions of irregular rigid bodies. It is certainly on the todo list, but this time we will be writing the collision code from scratch ourselves to better integrate with other scales. That takes longer than five minutes and a snack, so we will do it when we get to that point.