Ya know what? I'll just go with a picked number at random and finally end this:
Let's go with I think a fitting % for Jigglypuff here, 128%, since she's so light.
Now then, based on what was shown in the one image last page, and several bits of info before, the amount is about either 0.25 or 0.10 damage-wise on how far you go if you hold a specific direction. As such, this is how the math adds up:
128.00 - (128.00 * 0.10) = 115.20
128.00 - (128.00 * 0.25) = 96.00
As such, if the reduction is 0.10, then a Jigglypuff at 128% damage-kill% would live at 115.2%, and if at 0.25, then it would be living at 96%.
So in other words, the fairer of the two is clearly the 0.10 reduction, if all is correct currently. And by then, ya only need one more good hit to take them out when you land one to get the job done.
And as for directions being added to the mix, that's an easy one: point in the direction with more space, and thus less pain. But this then means more incentive to then have the attacker desire the other player to keep closer to the side edge, especially for grabs, smashes and the like. So there's that to also consider.
tl;dr: There is A LOT to consider here, with both mathmatical, competitive, and simple logical facts pointing out one thing: this can actually go well, and be quite an interesting new twist/change for the game, and how battles go. And yes, campers will exists (and they always will), but for the majority of us, I think there's potential for some exciting smashing fun here.
Or in other, more cheesy words: THEM'S GOLD IN THEM THAR VECTORS