You can already get Dex to damage in PF, but it is limited to some weapon categories or classes (hello Stalker^^). Fencing grace allows dex damage for a rapier, Dervish Dance for a scimitar and Slashing grace allows the same for one light or one handed slashing weapon in addition to making the weapon do piercing damage as an option.
TWF right now is (from my experience) almost a rogue-only option since the rogue gives a damn about multiplicative +x damage per attack and wants to sneak as often as he can. Using a Two-handed weapon (as a fighter with that massive +hit from weapon training) with Power attack, a good crit range and a lot of STR is so, so, so much stronger and less feat expensive. But I guess 3.x editions and their derivatives are just a balancing hell since I can see your fear of making STR a dump stat when DEX becomes too good for combat.
TWF right now is (from my experience) almost a rogue-only option since the rogue gives a damn about multiplicative +x damage per attack and wants to sneak as often as he can. Using a Two-handed weapon (as a fighter with that massive +hit from weapon training) with Power attack, a good crit range and a lot of STR is so, so, so much stronger and less feat expensive. But I guess 3.x editions and their derivatives are just a balancing hell since I can see your fear of making STR a dump stat when DEX becomes too good for combat.