It seems like the RoS on Ironbreakers question needs to be answered a few different ways.
1: Will Ironbreakers with a 2+ armour save and a 6+ parry save be imbalanced by virtue of their toughness?
2: Will Ironbreakers with a 2+ armour save work too well with other Dwarf units? I don't want to start a furious anti-Skaven debate, but for example the Slave is a terrible unit. Awful statline, explodes when they flee and are pretty underwhelming. But when you factor in Strength in Numbers, generals leadership, reroll from BSB and Steadfast makes them pretty immovable. We need to consider if Ironbreakers with RoS would be too good in combination with our other units, since no army unit exists in isolation.
3: What should this unit cost if they're going to get this upgrade?
I was also just talking to a friend of mine and he had a really interesting idea that I think has a lot of promise. What if Ironbreakers caused reverse impact hits when they were charged? To represent how tough and fearsome they are? For example a unit of Orcs (5 wide) charges a unit of Ironbreakers (5 wide) and the Ironbreakers inflict 5 impact hits on the charging Orcs.
This would give them some extra punch when they get charged.