
Thusly, I begin my rant. Flame away!

Powerplant material: ilmor got it right with the beryllium engine, which got banned. It'd be interesting to see ceramics and plastics being used as the block material. Isuzu built a ceramic diesel back in '92, it's not impossible.
Powerplant layout: as has been mentioned previously, why not turn a V10 inside out, and have the engine breathe in from the *outside* of the vee, with the exhaust on the inboard side. This would allow even slimmer sidepods, and this layout is a perfect fit with the current (high) engine cover regulation.
I'm pretty sure BMW's valvetronic is already implemented, as is GDI (McLaren?)
Drivetrain design: Why don't Honda and Toyota employ hybrid electric designs? The extra 50-ish bhp boost available from a smallish electric motor is always welcome. I believe it's within the rules to design such an engine. The (possible) fuel savings is an added incentive.
Gearbox: So, is the twin clutch on or not? But it's nice to see carbon 'boxes finally working. And is it possible to install a hybrid wet clutch w/ lockup (the kind we see on modern slushboxes) and gain the benefit of the double clutch mechanism?
Well, I hope that should start some discussion.