[P-hack]

I like the idea, I don't understand all the losses in the hydraulic system but it looks like a promising approach for improving regenerative braking over modern electrical approaches by a huge margin, both in terms of overall efficiency and in terms of providing much more braking power and returning more of the captured energy.

Energy density isn't much of an issue if absorbtion is limited to %200 of a typical decel/accel cycle. Can swap in a larger accumulator if you have hills. Current electric regen is returned as a fraction of total braking energy. While it is convenient to use electric regen, that hardly makes it the most efficient choice. There is a lot of room for improvement and options beyond electrical, which has it's own limitations.

Still I wouldn't put it in-line with the ICE, not without understanding the losses. Coupled to the front wheels? absolutely (and it can still modulate engine load from there anyway)