While we may not know exactly what the designers had in mind, therefore might not "get it" per se. I do agree with Eby and chano.
I think the BRZ/86 was designed to be an economically priced sports coupe that handled really well, had decent power and minimal ancillary bits that could create havoc or upset the package either by its characteristics or by those component's perceived impact to warranty repairs/reliability. IMHO at least, when introducing a new concept that is a joint venture, I'd bet the last thing Toyota and Subaru would want is a rash of "glass tranny", "Failed turbo" or what have you. Not to mention there *may* be a learning curve for Toyota service on the boxer engine, which *could* effect customer service. (All hypothetical theories of course.. )
I personally believe there will be a higher horsepower version available. Many people obviously understand the theory of the car, and are in tune to what the designers had intended. However that is not to say that many of these same people would want more power in the platform, either from the factory or via aftermarket options.