Others may be able to add to this list, but horsepower limits will be determined by:
a. The marketplace maintaining a financial (expenditure) interest in high horsepower (probable)
b. Combined with whether the sale of such vehicles creates great revenue for the manufacturer (improbable)
c. And/or serve as a flagship that sells sedans, SUVs and trucks (possible)
d. Adding on: any increase in accident created insurance costs (likely)
e. Never forgetting: "left wing environmental wackos" who feel that children, eagles and wildlife preserves are forever lost if performance cars are driven on weekends.
In toto, I strongly believe that Ford looked long and hard at the GT-40 concept and as to whether it would positively impact the sales of their entire line. Similarly, I do not believe it is smooth sailing for the Corvette people to make a case to Chevrolet that this is the best use of development funds.
Perhaps the best question is:
Did my buying a DODGE Viper result in me buying or recommending other DODGE vehicles? In and of itself, the Viper is not something that would sustain a company (and may not be met with enthusiasm when there is German ownership. Remember that Germany routinely criticizes Americans for spending too much on what they consider frivolity).
Alas, decisions are made in board rooms based upon fiscal numbers, not the pleas of end users.
The auto show should tell us what the corporate thinking is. Personally, I would not swap for a Z06 based solely on horsepower, and I do not need/want creature comforts.