As many people already said, there's no difference between weapon size damage in the current playtest, but I think it implies in some design problems:
1: "Titan Mauler" class feature turns into a lot of counterintuitive situations: Striking without rage deals the same amount of damage as a medium and even small weapon. You need to found exactly large magical weapons in adventures or can't use your class feature.
2: It limits the design space for large or tiny PCs in the future, or generates the necessity to add rules in another book(s) other than the "Core Rulebook" (assuming that this continues for the definitive edition next year).
3: It generates confusion with the "Fighter" class progression weapon damage dice (1d4 > 1d6 > 1d8 > 1d10 > 1d12 > 1d12+2). Almost everyone I questioned about the "Titan Mauler" using this Fighter progression said: "Yes, use this for your large weapon".
I think the better solution for this problem is assuming the Fighter weapon damage progression as a rule for "tiny/large" weapons, while the magic weapon damage doesn't scale the "+2" after the 1d12.
Ex: Weapon +1 = 1d12+2
+2 = 2d12+2
+3 = 3d12+2
+4 = 4d12+2
+5 = 5d12+2
Yes, I know it adds more complexity for the rules and probably there's a better solution out there, but I'd like to know how you from Paizo and others players think about it.