Somewhat true, not completely true. The car will load-shift during lower-load periods to operate the engine at, say, 100HP when the user asks for 50HP, and use the other 50HP for charging. This is already done in hybrids and ER-EV's (you can see this in action in the Prius, which otherwise can't even climb a 5% grade at 65mph, the ActiveHybrid's SPORT mode, and the Chevy Volt's Mountain Mode), and typically you can ask for more aggressively topping off the battery (at the cost of fuel consumption) through a SPORT mode or the like, while the Comfort or Eco mode will pick a lower charge target so that it can regain more energy on a downhill stretch with regenerative braking.
Now, your statement is true in that if you continuously
ask for more power than the engine can produce, you will at some point "run out of juice" and your car will revert to a turbo-3-cyl. But given how big this battery is, you'll be pegged at the governed top speed for quite some time
Very rarely does a driver constantly ask for the peak power output out of the car for more than half a minute at best.
The Prius, for example can only boost for around half a mile under full throttle (see last sentence of http://en.wikipedia.org/wiki/Hybrid_...ve#Performance
). The ActiveHybrid 3/5 can provide around 20 seconds of boost (http://www.driving.ca/research-car/r...940/story.html
). Starting with 100% juice, I'm usually down to 90% after a full throttle 0-70. But remember the AH3 only has a 1 mile electric range, so the i8's battery is much much larger.
So yeah, if you are doing dyno runs on this car all day, sure, you risk running out of juice and being left with a 150HP "sports" car. On the bright side, it beats a dead Tesla at the side of the road, and somehow that's a "sports" car. But in reality, as soon as you let off on the throttle the car is going to load-shift to recharge the battery for your next lead-footed incident, so I highly doubt this will be a real world problem.