You would use pitch hitters.Watching pitchers attempt to hit does nothing for me.
The bench would matter.
If a starting pitcher went out after 5 or 6 innings the spot in the lineup would likely come up 1 or 2 times most games.
This rule change would incorporate both leagues rules and make SP matter.
It would cause these openers to become less frequent or force teams to put who they wanted to DH in the field.