"It's bad/much harder for reliability" - Completely untrue. The systems involved in putting engine power through a transmission, and to the wheels, are exactly the same. The packaging may be different than what you see on a "typical" mid-engine LMP. The only argument for this idea is that the front tires would experience more wear, but this can be mitigated with setup. As someone who has raced FWD touring cars, I can tell you that wear can be made pretty even with the right set up, especially if your primary goal is longevity over outright pace.
"and [FWD] was the reason for maybe half their 20 second per lap deficit (traction out of corners, instability under braking, high speed cornering dynamics)" - Thats a pretty bold statement based of a lot of assumptions. The traction out of corners was largely a set up problem. On their later stints, they were not experiencing anywhere near the judder and wheel hop they had at the start. The instability under braking is just flat out false. There is nothing to suggest that at all whatsoever. Most all of their braking problems were a result of not having any kind of kinetic harvesting to off set it, and the braking package they went with, being a "this is what we've got" compromise. They also did no appear to have any issue in high speed cornering. With the Porsche curves being the sole exception to that, because of the high loads. That is easily a chassis setup issue, and not a FWD issue.
"a) they have to get it working perfectly at maximum power/duration to balance the car" - How is this different from any other team? Clearly Audi lost theirs, and it fouled up their car pretty horribly too, in terms of pace. So this seems a bit pedantic.
"b) they have to get the complicated system - including rear transmission - down to weight limit" - This has kind of already been done. The development for most of this has already been taken into consideration. The issues are in the FlyBrid system itself. Actually getting the power to the rear wheels will be a straightforward task, as its already been largely designed into the chassis layout.
"c) they have to make it all reliable" - That issue falls on ToroTrak at this point, not Nissan. Their vender is letting them down at this point. Not exactly within Nissans control. Nissan came to them with a design idea, they agreed it was feasible, and they havent delivered on that agreement. I wouldnt be surprised if Nissan switched to a different flywheel system, from an alternate vendor, like Williams, for example.
"d) they need to stop losing so much time when the system is off because 1) it won't be on for 150 to 180 seconds around a lap - some of it through turns, 2) Audi lose much less time when their hybrid system stops working" - Keep in mind, the loss of time is a compounding problem. A: They are carrying around additional weight in a hybrid system that isnt functioning. B: They have limited chassis set up time, and all the issues that come with it C: Thae chassis setup led to traction limitations out of slow corner, which was further compounded by cars WITH functioning hybrid systems. You can almost count the individual seconds in the acceleration phase of slow corners just by applying some basic logic. And the more the issues compound, the more time they hemorrhage, the sum of the whole being greater than the individual parts, and what not. And lets keep in mind that Audi has a HUGE history of chassis setup from which to dwell from, and still an amazing engine program to back that up, despite the loss of their hybrid system. power. Its no wonder they were still faster, they have a FAR more refined car.
Not trying to bust your chops, but point out a lot of the logical fallacies that people seem to have in regards to the car being FWD, and why they are incorrect, and why they deserve to be examined from a more logical engineering viewpoint.
Porsche 919 by Matt Stokes, on Flickr
Nismo GT-R LM by Matt Stokes, on Flickr
Porsche 911 by Matt Stokes, on Flickr
Oops by Matt Stokes, on Flickr
Thursday Night Qually by Matt Stokes, on Flickr
Sunset by Matt Stokes, on Flickr
Toyota TS040 by Matt Stokes, on Flickr
Corvette by Matt Stokes, on Flickr
Beausejour by Matt Stokes, on Flickr
seriously, maybe <10% were alright.![[Nor]MclarenF1](/forum/data/avatars/m/169/169289.jpg?1413287138){kind=avatar}
So glad you guys are OK. 
