The easiest way (IMHO) to give the systemd/nspawn container an own IP in the home network of the user, is to connect the container to a (software) bridge. For that, the user has to create such a bridge and connect the main network device to this bridge. For more details see https://wiki.archlinux.org/index.php/Network_bridge and https://wiki.debian.org/BridgeNetworkConnections.
Note, that the main network device may loose its IP when it is connected to a bridge. No guarantuees. Use these hints on your own risk.
In my case, I had to change /etc/network/interfaces on the host like this. This is individual on every server.
auto br_wired
auto p12p4
iface p12p4 inet manual
iface br_wired inet static
bridge_ports p12p4
address 192.168.0.2
netmask 255.255.255.0
gateway 192.168.0.1
dns-nameservers 192.168.0.1 8.8.8.8
When you are connected to the server remotely, it is best to do something like this:
screen
cd /etc/network
cp interfaces interfaces_working
# now change interfaces
# now we need to apply the new configuration. When the connection drops, the network gets restarted automatically. If the connection still works, the user can cancel 'sleep 60' with CTRL+C. Note, no guarantee that this works.
/etc/init.d/networking restart && sleep 60 && cp interfaces_working interfaces && /etc/init.d/networking restart
Now the software bridge br_wired is connected to my home network. Connecting a systemd/nspawn container to my home network is now as simple as systemd-nspawn ... --network-bridge=br_wired.
For more details, consult man systemd-nspawn.