Maybe I can report next year on the fun and games to be experienced when moving from copper/DSL to glass-fibre … 
- I’ll see if 1&1 (United Internet) can deliver a FRITZ!Box 5590 Fiber set up for our ISP connection or, whatever, in time for the cut-over …
Several days of operation revealed DNS of the 7530 AX still being shaky. Enabled avahi-dnsconfd and got stable operation of host erlangen:
**6700k:~ #** host erlangen
erlangen.fritz.box has address 192.168.178.27
erlangen.fritz.box has IPv6 address 2001:..............................
**6700k:~ #**
Another week of operation made me try out again NetworkManager. In the past it had exhibited annoying behaviour and proved unstable. None of the past issues occur with the current version. Thus I now go with the default network settings.
Tumbleweed has improved vastly since my first install in August 2016. These days I successfully dropped all of the local patches to the system:
erlangen:~ # systemd-delta --type overridden
0 overridden configuration files found.
erlangen:~ #
Kudos to the maintainers!