Idk what they are gonna change with the 3x bonus for rogue daggers but backstab formula is:
Backstab skill / 25 = mod times main hand dmg value, so for example say with say 250 backstab skill and a 15 dmg main hand dagger your backstab would hit for up to 250/25 = 10 x 15 or 150 dmg.
Then you apply non piercing modifier of 75% or 2h modifier of 50%, then factor in other combat modifiers, bonuses, aa, crit, etc.
Because backstab is based on main hand dmg and because of this reason 1h piercing weapons are artificially low this is why 2h is always better than 1h or 1h piercing. A 2h that does 110 dmg x 50% is 55, so you would need a dagger with 55 dmg or higher to match it.
I'm guessing that the 3x bonus is just a straight up 3x base dmg in the formula to make daggers better for backstab than 2hers. Palladium is like 118, or equivalent to a 59 dmg dagger. With a 3x bonus on the current top end daggers at 30 you end up with 90 equivalent.