3 months have gone by since this thread was opened and still no tvheadend for focal fossa under unstable at
http://apt.tvheadend.org/unstable/dists/
. It's a bit weird, since even the development team writes "Development is the recommended choice for most people as Stable is very out-of-date at the moment".
The only site providing tvheadend for actual Ubuntu distros is
https://launchpad.net/~mamarley/+archive/ubuntu/tvheadend-git
.
Pity, as I always prefer to install from the original site, but thanks a lot to Michael Marley, or users running Ubuntu >18.04 would still be running old tvheadend releases.