So I have a couple thousand miles on the FR-S now (not my car in pic, mine is stock) and am beginning to understand the car a bit better. I read about how the FR-S/BRZ were built to be modified, how the platform supports customization and is a blank canvas for owners to make the car their own. But after driving the car for some time, I'm not so sure this is true, at least for performance modifications.
The FR-S is an extraordinarily balanced car. Meaning that suspension characteristics are balanced with transmission and engine power, power delivery is balanced with the suspension and stock tire design, weight is balanced with suspension, gearing, and power. The car reminds me of the S2000, in that it is highly engineered and balanced, and modifications often don't improve performance, in fact they often upset the balance of the car and make it perform worse overall. Yes, you might improve 0 to 60 time, or cornering grip, etc but the overall balance of the car can be easily upset.
Somebody asked me recently how I liked the FR-S so far, and I said that it is a rare car that is greater than the sum of its parts. This is because of the finely engineered balance, like a carefully tuned piano. Japanese cars are often criticized for lacking character or soul, because they don't have any obvious, overt characteristics like cartoon styling, or raucous snorting 707HP engines, or airplane sized wings. They also often don't have any glaring faults that also give a car personality, like a Jag leaking oil, or a Ferrari catching fire. So owners try to add personality with modifications, but doing so can sometimes end up with something worse overall than the original.
All of this makes me wonder if the platform wasn't made for modification, at least not major performance modifications. Adding a turbo or supercharger would surely upset the balance, requiring appropriate modifications in other areas to restore balance. People say that Toyota/Subaru have not added a turbo option because they intend for the aftermarket to do this, and for users to upgrade as they choose. I think they are not doing a turbo because the current 200HP NA boxer is a critical puzzle piece in the engineering solution. Adding a turbo means, upgrading the clutch, transmission, diff, axles, tires & wheels, intercooler and plumbing, brakes, and suspension. At what cost in weight and dollars? So you have a 270HP, 3100lb, $32k car that handles worse? I don't think I want that.
I may not be the typical FR-S/BRZ buyer. I'm middle aged and own/owned a number of performance cars, some very fast. I bought the FR-S because it is so well balanced and is one of the best 'pure' sports cars you can buy right now. I think I will keep the FR-S stock for now, and consider any performance modifications very carefully.