I have a friend who worked in the game industry in Sweden for a decade or so, and said he heard this house rule from a friend at FFG. I have suggested it to my game group and they loved it immediately. No more frustration over misses. What do we do? Instead of interpreting the X as a miss, we use it as a multiplier.
We felt it worked well without altering present mechanics or theme. The defender doubles their shields rolled when the attacker rolls an X. Pierce is counted only after shields are doubled. If a poorly executed attack comes against and equally poorly made block, someone could still get hurt ...
In 3 or 4 quests played this way, I think damage has been dealt on X's 5 or 6 times, and on one particular roll, a full health monster, a minion zombie, was killed with an X roll. Even the OL felt like the zombie deserved it after the power dice were rolled so well.