There will ALWAYS be a market for wretched excess, so you are going to see supercars with higher top speeds and ungoldy horepower/torque ratings. There's always going to be that 'mine's bigger/faster/more powerful/etc. than yours' group craving that. Never mind the fact the car will never be used to even a small percentage of its potential- some guys just want to be the baddest on the block.
As far as seeing supercars built and intended as strictly race-only, I don't know if that willl happen on a huge scale. You might see some with opition packages which are racing-oriented (in fact, there already are a handful of cars that can be equipped that way) but it won't be the main intent of the vehicle when it's being designed. I think it might go the other way though- you might see more reasonably-equipped (for day-to-day use) cars being introduced, and more performance-oriented versions of existing car lines. Who knows- maybe we've already reached the pinnacle of supercar performance as far as horsepower and top speed go, and they'll focus more on handling and day-to-day operation instead. Whatever happens, it will be cool to see it unfold.