Very nice review, and some excellent sample images!
Three minor points/corrections to mention:
1) The 100-400L was intorduced in 1998.
2) Regarding weather sealing, although the 100-400L lacks the rubber gasket at the lens mount, the rest of the lens is actually weather-sealed, including the switches and the zoom/focus ring. Actually, that's true for all of the pre-1999 white EF lenses (200/1.8L, 300/2.8L, 300/4L, 300/4L IS, 400/2.8L, 400/5.6L, 500/4.5L, 600/4L, 35-350/3.5-5.6L, 70-200/2.8L, and 100-400/4.5-5.6L). So I'd call it a 'partially sealed' lens.
3) You mention that AF isn't possible with the 2x extender, that applies to SIR phase detect (dedicated AF sensor) only. Contrast detect AF (Live View) and the 70D's dual-pixel CMOS AF (which uses the image sensor for phase detect) will autofocus with an f/11 lens.