A new and completely non-revolutionary all-metal hotend design

The Reprappers' fever has finally got to me and I just HAVE to design my own hotend. Because. You know. All commercially available hotends are awful and/or too expensive. I am sure they can be improved upon. Any kindergartner could come up with a better design!
If it works, I would like to sell it. A friend of mine has a machine shop with a few CNC machines, so we can make small production runs.

Design considerations:

• Must be able to handle high-temperature extrusions (>=300ºC)
• 1.75mm filament (I think 1.75mm is the future)
• Use with standard type or with bowden-style extruder
• Low cost
• Raw materials can be easily obtained at a good price
• Easy to take apart
• Easy to clean
• Simple construction
• Few custom machined parts
• Keep machining times short 
• Minimize tool-changes
• Precise
• Deliver high-quality extrusions

1. Barrel
For high-temp extrusions the conventional wisdom is to use stainless steel for the barrel. Why? AFAIK there are several reasons:

• It can handle high temperatures (PTFE and PEEK can only handle up to 250ºC)
• It won't corrode when used in a hotend
• It's pretty strong
• It has reasonably low thermal conductivity ( around 14-16 W/mºC for ASTM A269)

McMaster offers an interesting looking seamless stainless steel tube with OD 4mm and ID 2mm. Perfect. 1.75mm filament will fit nicely and we can just connect it at the cold side to a 4mm OD PTFE tube with a compression or push-to-connect fitting for a bowden extruder. 
Unfortunately Stainless is not the easiest metal to machine, so we should try and keep the machining of it to a minimum.

Then we need a heater block, a nozzle and a heatsink. 

2. Heater block and nozzle
In order to keep things simple, we'll keep the nozzle as part of the heater block for now. Similar to the J-head extruder. This makes it harder to change nozzle size, but will keep machining, and thus cost, down.

3. Heatsink
The heatsink has the job of keeping the transition zone as short as possible. It is made from aluminum and held at the bottom by a nut and at the top by a clamp. 

The whole thing should look something like this