Here are some points:
There is no way the firmware reflash "went wrong" or is corrupt. The images are encrypted and signed in such a way that if even one bit is altered it will not flash. If the flash memory in the ECU had failed in such a way to alter it's code, the checksum algorithm would catch it and it would hard fault.
The dealer computer tool (Consult III+) will not allow a firmware regression, nor will it "reflash". (even if this could help) It's basically automatic, and out of the dealer's control. Only Nissan Engineering with special development access can manually perform any ECU flashing/reading.
Consult III+ will list all firmware versions (ECU part #'s).
While the reverse lockout problem is indeed an apparent firmware bug, and Nissan is likely very aware of it, these other problems sound like something else. My bet is one of the devices on the CAN bus is flaky and creating errors on that bus which is causing the strange intermittent symptoms. As pointed out, simple module swapping would eventually correct the problem, but a detailed CAN analysis would probably reveal the problem pretty fast. However, Dealer techs are not able to do more than basic go/no-go testing using Consult III+. This would require a visit from the Nissan Engineering Team. It may be that because they have already labelled this case the "known reverse incline lockout bug", they are ignoring further information that is indeed a new and different problem.
Keep in mind most customers are poor at providing good information and there are also many layers between a customer and someone at Nissan that is an actual Engineer, so it's not surprising that this is happening. Most customers simply make a bunch of noise and are poor sources of information, so Dealer Techs and even Nissan corporate learn to generally filter much of what is heard and form their own opinions which means even if you know what you are talking about, and give good information, you will probably not really be heard.
So in summation: There may be a small known problem with the reverse lockout thing, and I'm sure Nissan will fix it in an upcoming firmware update, but they are very careful about updating code, and only do it after many, many hours of testing. Don't expect fixes any more than once a year at best unless it's a total emergency. I do not think this problem is a firmware-related issue, and while it coincided with the update, I do not believe regressing to an old version (even if it were possible) would fix this. I'm fairly confident it will need module replacement. It's possible there was something as trivial as an ESD (Electro-static discharge) that might have damaged a module. (Maybe while in the Dealer's care for the update)
I would persist with the Lemon Law claim to force them to act on this. It's inexcusable, and this combined with how Nissan has been treating the Phoenix battery issue definitely lowers my opinion of them. I am very dismayed and disappointed in this kind of surprising poor performance from a Major Japanese automaker. I hope they step up soon.