Some great ideas in there for sure! My comments:
The Filabot Wee's Bill of Materials is estimated at $244 before shipping when purchased in bulk, and it requires welding/machining. I haven't seen more than a few dozen feet come out of it, but I've heard it works okay. To my knowledge it has not been tested by anyone but the creator.
Lyman's Filament Extruder requires less machining, but costs $240 in bulk. To my knowledge, kits/assembled extruders are not being sold by Mr. Lyman. I drew a lot of inspiration from Mr. Lyman's design, though in the end I only kept 2-3 parts from his BOM. To my knowledge it has not been tested by anyone but the creator, but it seems like a great design that would work well.
The other extruder (posted by doctorcontra) I had not seen before. It appears to use a National Instruments USB-6009 for control. I use these at work - they're $200 a pop. He uses a bigger, high-current heater (15A) which is more costly to modulate. I would estimate his BOM at nearing $500.
He's using a set of die rollers, which is an interesting idea. I know Ian was looking into things like this quite a bit. I'm not entirely clear on how he's controlling them he talks about PID controllers, but I can't make out the info on his block diagrams. Maybe he explained it and I missed it. It's still really interesting!
One of the big issues here is cost. In my opinion, people won't pay $400 for a filament extruder - $400 buys almost 20lbs of filament, enough for a couple years for most people. $400 is also almost enough for a printer! At $200, things become a little more attractive. I've worked hard to get it to that price point, spent many hours tweaking the BOM. The Filastruder is a full kit, requiring only a Dremel, drill, and basic hand tools to assemble - no welding or milling. That, in my opinion, sets it apart.