The Micro-bolometer sensor in the 570 is huge. I suspect as technology has progressed, the size has been dramatically reduced, as in the video of the Indigo security camera. I believe sensitivity increased as well. The large lumps of Germanium in my cameras makes for very expensive manufacturing costs in terms of both the actual lenses, and the heavy duty mounts required to hold or move them.
I am very much looking forward to seeing the thermal engine used in the E4. I expect significant miniaturisation and simplification of the optics/shutter assembly
IIRC FLIR told me that the 570 Micro-bolometer is actually heated and stabilised at a temperature of 30 Degrees C (?) using a Peltier element. I have never confirmed that though.
The ergonomics of the E4 case and the lighter weight does appeal. My FLIR PM series are more like heavy camcorders in comparison. BUT they are still gorgeous bits of kit, built to last and provide superb thermal images. Maybe I will sell one and buy a more modern unit for mobile use.