It is certainly not out of the question...my guess is they will stick with a very similar powertrain setup for the next generation, albeit with a minor power bumb...470 is definitely possible though. Since it is almost certain that they won't go the FI route yet, I would love to see Toyota focus on some weight savings and a better 50:50 weight distribution for the next gen ISF. Even if BMW and MB trump the ISF with crazy power for the M3 and C63, I think I would hands down prefer a lighter, more powerful, and better chassis version of the current ISF. If the ISF could get 470bhp and drop weight to 3600 lbs, that would be awesome, and easily doable for Toyota w/o a lot of R&D. That would yield a power to weight ratio of 7.66 lbs/bhp vs the current 9.09 lbs/bhp. It would be less evolutionary than the Germans, but would yield equally impressive results while using a tried and true powertrain that gets decent fuel economy for what class of car it is. If Lexus made these few changes, the next gen ISF would be capable of 11s stock and would be a track monster.
You made some very good points. To make anything go faster, it's either:
1. Shave weight.
2. Increase the power.
I don't know how they can save 100 lbs, they'd have to lose something. Being it's a luxury car, they would have to get creative.
The simple math of 416/5 = 83.2 horsepower per liter.
The engine is already 11.8:1 compression, I don't know how much more they can squeeze out of it.
I do agree with you that I don't see them going with forced induction, I'd be very very surprised if they did.
I really don't understand why they didn't start with the Tundra 5.7L unit, but hey, it's not too late isn't it?
5.7L x 83.2 hp/L = 474 horsepower.
If they shorten the stroke, they can get more RPM out of the engine. Higher flowing exhaust and headers can also help and of course some work with the ECU.
I guess time will tell.