The trouble with more tire is you can argue it becomes less fun. The cool thing about the FT86 is that on its crappy tires it has enough power to hang the tail out and have fun. You can't toss our cars around like you can a BRZ/FRS, and that is what makes them fun.
If you put some wide, grippy rubber on then all you have is a car that feels like it corners on rails with an on/off throttle switch. Boring!
Now, if they decided to give it 300 hp, yeah, lets put more tire on... but as it is now I like the balance. Forget speed, hello fun.