Upgrading to Fedora 26 was very smooth. The one change I had to do was because I use the Terminus font. In Fedora 26, the font name changed so in the apps where I’ve picked Terminus, I had to change it to the new name (terminal and conky).
On one system that is connected to a TV through HDMI the login screen has the wrong refresh rate and resolution. I haven’t figured it out yet.