I play a lot of co-op multiplayer. In fact, 70-90% of my TWWH3 game time is co-op multiplayer capaigns.
It's getting pretty frustrating that a key feature of the Herald type daemon lords is still not working in mutliplayer.
Extra galling now that mortal lords can ascend into princes in multiplayer just fine if you're playing WoC (but not mono-daemons... which... I guess is a design matter rather than a bug.)
Just add the Path to Glory system framework to mono-daemons as a work around if necessary as a work around.
Or something similar to Be'lakor's shadow mechanic where you can apply a ticking timer buff to one of your lords and kill them and add a exalted daemon to your pool.
There must be plenty of ways to fix this bug if the current implementation is somehow only working in single player and needs a workaround.