Tom abrahams mentioned recently how the price of the 21mm SA was effected when cosina built a comparable offering. It went from the only game in town suddenly to a lens that appealed to a certain section of the market that were interested in its "flaws" since there was a "better" and well more affordable 21mm option on the market. Its somewhat logical to deduce that the price of a noct could be effected similarly if there were a new offering from another company that was of reasonably similar quality (saving a debate on whatever that is) for considerably less money. Its reasonable to think that the noct will relatively hold its value were that to happen however I would think the way the price has screamed through the roof would completely stop. If there was a cosina 50mm f1 lens that was decent enough for a handful of people out there, and it was available 18 months ago, we would probably not be seeing $5k noctilux right now.
If you think about it, a parallel comparison between the 21mm SA and a noctilux is pretty level, they are both "flawed" lenses that definitely appeal to people because of their look. The problem with the noct is that in addition to appealing to the people that like its unique look, it also appeals to every single other person that wants a F1 lens. If the market provides a lens that is way better than the canon f1 I think you'll see a lot of potential noctilux people that just want an F1 lens and dont care about the special noctilux look going that route and especially so if the lens is well lower priced, which it would almost certainly be if you consider the price of the average cosina lens. Once this happens, the noct is now reduced to where the current 21mm SA is, its an awesome lens, its still in demand, however the only people using it are people that understand it and WANT to use it, someone that just wants a 21mm can get one for $300 and not pay the premium on the SA. There's less people in the market now and the high price just cant sustain itself. I got my SA for $600, which is a deal, but flatly impossible years ago. The guy that sold it to me "upgraded" to a newer 21mm from cosina.
Paying $5k for a noct now, to not use it, to me is insane as the instant someone makes a new f1, your "investment" is in trouble. Of course this may never happen, but if I owned a lens company and looked at the demand for noct, I'd certainly be spending my r&d budget for the next while on figuring out a f1 lens. Not everyone that bought a noct wanted a noct, they just wanted F1 and they didnt like the canon...
I know the original poster inquired about camera bodies, but I think this could apply to the discussion.