I like the idea of flanking. But giving away so many advantages at once sounds unbalanced (bounded accuracy makes it even worse - now your 5th level fighter has no chance against a bunch of kobolds). Also, if I to mess around with those cool flanking rules, I would still be playing 4e, right? To be honest, I don't even use a grid.
I also like the idea of facing. It just makes sense to me. But it is all a bit too fiddly. Also, if I wanted those nifty facing rules, I would still be playing 3e, right?
Who am I fooling, I don't even use miniatures in most of my games...
But - wait! What if flanking IS facing?
|Wayne Reynolds, Copyright Paizo.|
If a character gets surrounded by two or more creatures (or vice-versa), the creatures can divide themselves in two groups in order to flank/back-stab the character. The character chooses which group to face. The other group has advantage when attacking the character. The number of creatures that can attack a character at once is limited by their size, position (no backstabbing people who have their backs to a wall), and the length of their weapons.
No need for minis, grids, "drawing diagonal lines" or more than one paragraph, really. Giving advantage to only half the attackers makes things a lot more balanced, and letting the victim choose is even better. And flanking becomes a bit more interesting because it now involves some tactical choice: do you give advantage to the big boss or all his annoying minions?