The Katana is fine doing bastard sword damage. I hope Paizo doesn't change it.
Just because the numbers are the same doesn't mean the weapons are, the weapons are completely different, but when you look at it from a stat perspective, the numbers even out.
For example, European blades are big and heavy. They do damage based more on the mass side of the force equation. In fact, the blades themselves weren't edged at all, they were blunted and designed to hammer into armor wielding opponents and shields without chipping or shattering.
The katana was designed more to shear through unarmored flesh, bone, or to cut through the lighter Japanese armor of the period.
From a balance perspective, the effect of wielding a katana against a setting appropriate opponent will be just as effective damage wise as a bastard sword would be against a euro-centric opponent wearing metal armor.
So should a plate wearing foe get a minor DR bonus or something against a katana? You could make a case for that. But conversely, against an unarmored foe, the katana is a far more dangerous weapon than a bastard sword. So if Paizo does do something like reduce the damage to d8, then I think the katana should get something like double strength damage vs. any opponent or monster not wearing metal armor to compensate.
Otherwise, just keeping the stats the same as bastard sword stats is a fair compromise.