Why you are not going to get a desktop SLS printer*

Preface:  The first patent ever (owned by Carl R. Deckard)  issued towards Selective Laser Sintering is going to expire in 2014. Because of that, a few popular magazines wrote articles about it, saying that these (or more exactly, this) patent(s) is "holding back SLS from getting to the hobbyists".

To be honest, this is just wrong. I tried to collect the reasons why you won't get a SLS printer for your desk, and compile them into the following list. Feel free to comment on it, and discuss it with me.

1. Cost - Divided into the different parts that make the printer that expensive
• Laser
No, the laser is not going to get cheaper only because some patents, which aren't even related to it, are going to expire. Maybe the price of an appropriate laser will sink a bit, because the demand increases, but that's not going to make a huge difference. Just taking a less expensive one is not going to work because you need:
• Accuracy
• The right power
• A good focus
• Powder
Here it's already more likely that the price is going to drop over time. The problem is that you can't just take "some powder". You'll need a material that fulfills the following:
• thermal conductivity
• thermal capacity
• viscosity
• flowability
• grain size distribution
in the right amount. There is a reason, why people write their PhD about the topic of finding new usable powders.
• Heating Chamber
If you want to print fast (read: efficient), the whole printing area should already be near the sintering point of the powder, which lies around 180°C (depending on the powder). Now that you have a functional and accurate (yes, 1 degree does make a difference) heating chamber, have fun isolating it.
• Gas
You are going to inert nitrogen into the building area, because the powder would react with oxygen at the temperature you print at. That would influence the quality you are able to achieve heavily.
Did I mention that you have to pay that gas? And you should also store it appropriately, because nobody likes to suffocate.
• Leakless building chamber
If you are going to inert nitrogen into the building chamber, please make it leakless. Better for everyone.
2. Size - Sounds weird, but there is a reason why the current printers are that big
• Powder storage
The powder distribution system has a huge advantage (you don't need supports), but also the disadvantage that you need about double the size of the printing bed as footprint. (Why's that you ask? I'm going to answer that in the "How SLS works"-post).
• Heating Chamber
It's hot in there. You should isolate it. Unfortunately, that takes even more space up.
• Laser
If you get a powerful laser, you are probably going to get a whole processing-unit with it. That thing isn't too small either!
• Cost efficiency (While this applies to the machines we have right now, you can probably ignore that for the hobbyists version of it (if it will ever exist).
To be cost efficient, you should print as much stuff as only possible at the same time. This is easier if you have a bigger printing area. Furthermore, you can print bigger (= more expensive) stuff on a bigger machine.
3. Various - Even more reasons againt something I want. Damn!
• Mess
After your print finished, you should get your parts out of the machine. Which is full of powder now. Welp, that's going to be a mess. In your workspace.

• Powder
The particles of the powder you use are small enough to be breathed, what's pretty bad for your health. Also, they are going to fly everywhere.
• Gas
Do you really want a big bottle of nitrogen in your workspace?
• Calibration
You thought that the calibration of your FDM printer is annoying and difficult? I feel like it would be much more difficult if you had to calibrate:
• laser
• powder distribution system
• heating chamber
All these points are important, and influence the quality of the part you get out of your hypothetical machine.
• Powder recycling station
Because the part you just created was sintered, and the space where the powder is, was hot, these particles are sticking to each other as well. This has two consequences:
• You have to filter the used powder to get the sintered particles out of the "good" powder.
• You need huge amounts of powder, because you are throwing big parts of it away after every print.
• Lead time
Chances are that noone really started the development of a DIY-SLS printer. I guess you should expect a waiting time (if you will ever get such a printer).
• Patents
Did you really believe that the ur-patent from Mr. Deckard was the only patent on SLS?

That being said, I would love it if I had a dektop-SLS-printer. I am simply trying to get some real arguments into the discussion.

*depending on your definition of "desktop", the possibility that we might get such a printer exists. It's still very unlikely.