If not every hit, how about an increased crit rate for all hits in the next WS, or the next attack round. Something like +50% crit for the second hit in your WS, +40% for the third, etc.

As for sneak attack being landable from any angle, well, it's not exactly a sneak attack if you do it in the mob's face. However, I would be pretty satisfied with letting sneak attack work from every angle *except* a 30% cone in the front of the enemy.

Both those would be for main thief of course. Maybe subbed thief could get an increased crit rate from SA as well, but not nearly as much. How often do you see people sub thief for damage anyway?