I'm not taking a look at the (usually ridiculous) Depth of Field argument. I'm more interested in trying to understand why these lenses work and why anyone but a professional would buy one. My gut feeling is--if you complain about the price, you don't know how or don't have a way to make money with the lens.
I'm not a portrait photographer, though I've tried modeling-type photography, and I've done many what I'll call quick portraits. When I'm photographing high school sports, it's often easy and desirable to get a quick portrait of the athletes. I often do this with either of two lenses which have effective 135 format ranges of 70-200mm for one and 100-400mm for the other. Using them at about 1 meter/3.3 feet works well.
The 135 format has had an 85mm lens for portraiture for a while. Canon has an f/1.2 lens and Nikon has an f/1.4 lens. Barely touching on Depth of Field, we don't want it so thin that only the nose is in focus, unless we're working in reconstructive surgery, of course. Of course, at a distance, it's less likely that we'll isolate facial features and likely that we'll just isolate our subject.
I'd suggest that any of these lenses are going to do the job, although I wonder which will do it best. It's becoming more difficult to find really bad lenses, unlike 10 years ago and earlier. For those who really feel that they want to pick up a 30 year old lens because it was great, you might want to re-think that. I'd suggest that any lens was great because it was better than other available lenses from the time and had a photographer been given current equipment, he'd likely never go back.
- Canon 85mm f/1.2 US$2199.00
- Nikon 85mm f/1.4 US$1699.95
- Nikon 1 32mm f/1.2 US$899.95
- FujiFilm 56mm f/1.2 US$999.99
- Panasonic/Leica 42.5mm f/1.2 US$1599.99
Besides these few, there is also the Samyang/Rokinon/Bower 85mm f/1.4 lens that generally (there may be a Nikon version having a focus confirmation) has no electronics with an exceptionally low price, US$349.99, I believe. This one exists for many mounts. It's not likely to be used as a backup for a wedding photographer's main system, just because it has no electronics.
The prices of the Nikon 1 system, FujiFilm X-system, and Panasonic/Leica micro Four-Thirds lenses are quite high, but they do have a rather large maximum aperture at f/1.2. Shooting in natural light will be enhanced, as you'll be able to shoot at more difficult times.
It's a bit surprising that the Panasonic/Leica lens is somewhat larger than the FujiFilm lens, but I'm hoping that the companies have put more effort into resolving optical anomalies optically, rather than through software tricks, even though Panasonic was recently given an award for their software tricks. Is FujiFilm's lens too small to be optically amazing and will it need tricks to correct for optical problems?
Obviously, the Nikon 1-system lens is the odd man out. I don't expect professionals to be using the system, but it could be handy. That said, US$899.95 is a large price for "handy".
If I were leaning toward buying a combination at the moment, I'd buy the FujiFilm X-E2 with their lens. While my first guess is that the Panasonic/Leica design is better (to go with the price), the GX7 is too small and the GH3 isn't good enough photographically to make use of the lens. Of course, there is the Olympus E-M1 and it is much better than the GH3 and rather a bit larger than the GX7. However, the FujiFilm combination ($2399.98 X-E2 vs $2999.98 E-M1) is less expensive and the sensor has much more to it (ignoring size, concentrating on the filter pattern), especially if raw development software can take advantage of the advantages it offers. At roughly US$4100, the Nikon Df and Nikkor 85mm f/1.4G lens would be a high image quality alternative, with the sensor and the image processor of the D4. It all depends on how little depth of field you really need. See what I wrote here.
Of course, a wedding photographer is probably already equipped with a Nikon D800 or Canon 5DMkIII and won't need another system but it would be useful to keep another focal length at the ready, without much weight involved. I often keep the Panasonic GH3 around my neck while using the Olympus E-5, so I can cover telephoto and wide views.
Update 2014.03.16: I've seen a few people rate the FujiFilm and Leica/Panasonic lenses and they are both rated very well. I wonder how they would be rated if they were switched to the people who rated the other brand well. For US$999.99, I'd feel a bit better if there were imperfections because finding imperfections at a full price of US$1599.99 would make me unhappy. I guess that explains why I have two lenses worth more than US$2000 each. They're practically flawless.
I bet the E-M1 and Leica/Panasonic lens would be amazing and matched well. Equally, the X-T1 and the 56mm lens would be matched well. The lower density sensor with FujiFilm bodies would equal better image quality, but which lens is actually better. In any case, who needs a dSLR to get those special wedding photos now?
Update 2014.03.19: FujiFilm lens review here and Leica/Panasonic lens review here. The Panasonic lens seems to be the slightest degree of better (except vignetting wide open), but is it US$600 better?
Update 2015.05.21: Recently, Panasonic introduced a budget portrait focal length lens: 42.5mm f/1.7 with Power OIS. At roughly US$400, it should be a good deal for the majority of users who don't need a more razor-thin depth of field.
Further back, FujiFilm introduced a different APD-version of their 56mm f/1.2 lens that produced a more pleasant bokeh. It's priced about the same as the Panasonic/Leica lens.