It seems a strange choice of opponent given that Chisora knocked Scott out in 6 and Deontay Wilder stopped him in 90 seconds.
As a world title defence it is IMO a very weak challenger, a level below WIlder's heavily criticized voluntaries of Szpilka and Duhaupass.
It also carries the risk of dulling Joshua's momentum if he takes substantially longer than Wilder to get Scott out of there.
I feel there isn't much up side to Scott as an opponent for a newly crowned World Champion. Or am I missing an angle??