[PS3]
I voted no because I think putting the power of choice in a player's hands is important.
Besides that, it's technically "impossible" due to their being no more buttons to utilize a 4th ability on controllers.
Obviously not an issue on PC with ~103 keys at one's disposal, but the game has set itself to be "identical" across all platforms. Adding a 4th ability to PC only would contradict that.
PC and PS3 players cannot play together, so it could be added just for PC players without it affecting console users. Setting that aside, I am sure there could be an alternate way of selecting abilities for the console users.
Besides, the power of choice is exercised in buying the abilities. If it were a balance issue, it would be one thing, but limitations for one platform should not affect others. At worst, one might have to pay double for each ability after the 3rd.