I'd be interested in this lens at 4-5k tops but at over 10k it's looking to be for highly paid sports pros only. I wish 3rd party would step up their game on the longer focal lengths as I feel it's where canon is ridiculous with pricing.
But it's because the market is so small that the prices are so high. Sure, there are hobbyists with the big L tele's, but most are pro's who make their money with it. In which case, they can pay the premium (just like wedding pro's were willing to pay $3500 for the 5d3 that now costs 20% less).
I mean, the tech in the lens is pretty great; you are getting a 200mm-560mm f/4-5.6 zoom basically. And while 200mm f/4 isn't very impressive, the trade-off (variable aperture) isn't worth it, since most aren't going to be using this at 200mm anyway.