The fewer actual changes we make to the rules, the better. Any actual rules change makes it harder to jump in. Personally, I feel there are two types of rules that can be changed:
1) They don't work, or at least don't play nicely, in the framework of Living Enworld. That's, for example, the source of the much-hated Craft Points.
2) They don't work, period. Gamebreaking stuff. Epic Spells, I'm looking at you guys, as far away as you may seem.
I don't feel that non-stacking criticals will break the game any more than stacking ones, despite the hyperbole SKR uses. With the choice between two rules that work, I think using the default rule is better overall.