My two main gripes about the 40K rules are that Morale is really non existent and ineffective and the rules for Cover are so "shallow" that you might as well not have cover at all and then, terrain is
just on the table for aesthetic reasons.

Morale

What if we make this much more effective and make units do an enforced "Fall Back" move? How about - Casualties are deducted from your Leadership value, then you have to throw that value or less, on
a D6. If you fail, you do an enforced Fall Back move, with no special rules applying and you can move freely next turn?

Cover

All Movement across Cover, whether Moving, Advancing or Charging is at half speed, for the move in which you cross the "threshold". You can only fire or be a target if you are 1 inch (or 2?) away from the edge of the terrain feature,