Will we have replacement for Thunderbird? The KDE project is working on Kube, an email client.
I'm okay using Thunderbird, but there are sometimes bugs and I think nowadays we can have a better experience with better integrated services.
So, it is interesting to see if there will be new alternatives. (No, please, no Electron app)
http://www.omgubuntu.co.uk/2017/07/kube-promising-email-client-kde-sees-new-release