I don't know what my JSS score was prior to March 2017, but it dipped down real low. I don't think a lot of freelancers are happy with the lack of transparency in the JSS algorithm.
Why not just create a better rating system and keep everything public. If the client wants to vent privately, let that be something seperate that is only viewable by Upwork, the freelancer and client. I've read too many cases of people rated highly publicly, while their JSS scores sink. This suggests to me that something is very wrong, and that the private vs public options are being misused. Unintended consequences perhaps.
The only consequence seems to be that freelancer who used to be able to convince clients to change their feedback are now unable to and thus come to the forums to claim that their score is unfair.