To me it seems a bit expensive... obviously I have no idea about IQ but...
Canon 100-400 f/4-5.6 $1600 (but at 400 the glass is half the size in area)
Sigma 100-300 f/4 aprox $1200 (as I remember)
Sigma 120-300 f/2.8 aprox $2000 (as I remember)
Sigma 300-800 f/5.6 aprox $7500 (different range i know, but 800 5.6 should have same size glass than 400 4... but its an 800mm)
Canon 70-200 f/2.8 aprox $2200
Canon 300mm f/4 IS aprox $1300
Canon 400mm f/5.6 aprox $1400
So to me without knowing anything about anything!! I would kina price in the 4-5000 range.
But thats just me... I will not buy this lens as i dont need it.
I would love a 70-200mm 2.8 that goes to a 140-400 5.6 with a 2xTC
Max, you are sort of comparing it to the wrong crowd of lenses. I'd look at it this way:
Canon 100-400 f/4-5.6 L IS - $1800 listed - is 5.6 at 400mm and thus can't take 1.4x extender except on 1-series bodies, has older generation IS
Canon 400 f/4 DO IS - $6400 listed - is missing 200-399mm zoom range, requires separate 1.4x extender, questionable bokeh and image quality, has older generation IS, however it is much lighter
Canon 400 f/2.8 L IS II - expected $11000 listed - goes to f/2.8 but is missing 200-399mm zoom range, requires separate extenders
Nikon 200-400 f/4 AF-S VR - $6300 listed - requires separate 1.4x extender
that's really more the way the competition shapes up. so an approximately $7000 price tag seems fairly reasonable to expect