Now that Kubuntu 15.10 shipped yesterday, he's moving on and will no longer be serving as the Kubuntu release manager. Instead, Riddell is just going to get involved with upstream KDE development more as he no longer wants to be involved under the Ubuntu/Canonical umbrella.
Jonathan wrote on his announcement at Kubuntu.org, "for the last three years Ubuntu’s main sponsor Canonical has had a policy contrary to this and after much effort to try to rectify this it’s clear that isn’t going to happen. The Ubuntu leadership seems compliant with this so I find myself unable to continue helping a project that won’t obey its own community rules and I need to move on."
He also commented a bit more on ubuntu-devel, "I've heard from too many people who feel they have been bullied out of the project for this to be a personal problem. It needs a community council who will stand up for the third party and volunteer developers, who will criticise when money is collected for additional use of community but not used for this and who will ensure the Ubuntu policies on copyright licences are not in question and above all one that does not cause people to leave the project being felt they have been bullied out."
On Reddit, Riddell then claims that Canonical has "defrauded donors and broke the copyright licenses." It will be interesting to see the next steps for Kubuntu without Jonathan Riddell's involvement.