The teams had a good understanding of the largely unchanged hybrid rules 5 years ago, maybe further. I think it's safe to assume the legal limits of K delivery have already been met. 120kW whenever, wherever, for any duration. 8MJ K deploy min/lap. That achieved mainly through the "unlimited-unlimited" ES<>H<>K pathway. That should have been a dev target 5 years ago. Beyond that it's ICE and pressure charging. All further power gains being delivered through the piston conrods.
Ferrari were cracking intake manifolds last year. Perhaps they have a higher mass airflow system as Rosberg suggested. Turboshaft geared-up, flywheel effects of the rotating masses, impeller & housing design, etc.
There are really no power limits for the H. Why would this not be maximized. Why would the H not be 500hp at this point in time. Just throwing big numbers out there because the 40-60kW figure for the H keeps getting bandied about, which seems silly, really. The unlimited motor has half the power of the limited motor?
The H is how you deliver much more than 120kW from the ES to ICE. Via air pressure. If your ICE makes the supposed 700-800hp at 'normal' boost, surely a 500hp blast of air from the megacompressor would help you down the straights a bit. Plus the little kick from the 120kW K, of course.
Beyond flywheel and battery energy storage we might also consider compressed air storage. Storage would not be efficient unless highly compressed. The crankcase may be an option. That would be metered by the sump gas control scheme. Leakage of air through the piston rings near TDC would supply the crankcase with high pressure air. Reverse leakage from crankcase to cylinder would supply oil to the CC. Vented reservoir pressure would supply a power boost during acceleration. Since the crankcase pressure could be very high, similar to CC compression stroke pressure, the conveyance lines could be very small, and the reservoir supply duration lengthened.