Fed Up metamorphosis shocker
The new upgrade Tool, sef-deprecatingly named "fedup", is also coming good now.
For the first time in many years of "upgrading a linux distro", in Suse, Red Hat, Debian, Ubuntu, and Fedora (that's what I used, in order, since 1997) It went absolutely without a hitch, even though there are a fair number of customisations deviating from the default on my system.
Fedora's approach is a bit different from Debian/XXbuntu, the updater is a shell command that downloads all packages and installs a special "upgrader" boot image.
The updater feeds for many hours downloading the new versions for all my packages, including from 3rd party repositories. It's like a caterpillar eating and growing, but of course you can go on working until it's time to re-boot.
When you boot the FedUp image, the computer goes into the "chrysalis" stage where the system performs the updates, and emerges as a beautiful butterfly.
On Granny's Ubuntu box the update takes place with a pretty GUI and while the old system is still running, but it interrupts the work several times through the run with debconf asking questions, so you can't have it run while you're out.
Well done Fedora.