Righteous Fury is a curious game mechanic, allowing for what amounts to a critical hit regardless to how successful your roll to hit is (it can occur whether you have a large DoS or if you succeed by a few pips on the die). While I acknowledge that by virture of accumulationg DoS, a critical hit system is somewhat enacted (i.e. extra hits with Scatter or autofire). To appease my current batch of players, here is a game mechanic that we are currently playtesting:
The Eye of the Emperor
The Eye of the Emperor watches over all of his Children, whether they are in the midst of battle or engagining in the mundane tasks that ensure the Imperium's future.
When rolling a skill test, roll an addition d10 (here by deemed the Eye of the Emperor). If the test is successful and the Emperor's Eye is open (you rolled a 10), your test is a critical success! Should misfortune occur and you fail your test with the Emperor's Eye shut in shame (you rolled a 1), your test is deemed a fumble!
The actual applications of a critical/fumble requires a bit of GM judication, the intent is for flavor here, not actual game shattering mechanics. A small advantage or disadvantage warranted by the situation to spice the game up a bit. I concede this rule is superfluous and pointless, but it does seem to add some excitement to the game table. I allow the players to choose if they will roll the Emperor's Eye (its not everyone's cup of tea) and if needed, burn a fate point to avoid a fumble. I am aware that there is a DoF, but rarely is its use invoked (at the moment, I can't recall a single precedent of its use from the rule book). Should it please you, try this rule and enjoy!