I had installed quasselclient on my wayland system, but trying to start
quassel-client always failed. I don't have details anymore, but it was just a
segfault I believe.

Earlier today I installed keepassxc-full and that failed to launch too, but
it's error message was actually helpful and pointed me to the solution:
install qtwayland5. See https://bugs.debian.org/1136909

After installing that, quassel-client started to work too.
So it looks like quassel-client should at least Recommend qtwayland5 too.

Cheers,
  Diederik