So up until recently monster invasions were conducted by a few select players from the community, who I will call mods. These stopped happening because the mods said they were too much work and they didn't get enough thanks for the effort they put in. The players didn't always like them, many saw the invasions as being unfair, partially because they didn't affect every realm equally and partially because the invasion forces often couldn't be beaten conventionally, instead requiring some McGuffin device.
What if instead of instead of having mods lead invasions, you had regular players lead them? Regular players not already playing on Beluaterra could create a daimon character there, those daimon characters would be tasked with causing trouble for the humans. They would have separate mechanics from regular characters and would have to rely on their organisational skills and mechanics to make the most of limited resources at their disposal. This would mean that they could be defeated through conventional means.
Now here's the kicker: what if you didn't limit daimon invasions to Beluaterra, but allowed invasions wherever there was too much peace. Atamara, for instance. This could be a sub-game like adventuring, but for busting up hegemonies and gigantic realms.
I think that for Beluaterra this would be very fitting, not as a tool for busting hegemonies (that continent still has interesting politics), but for continuing the tradition of invasions, as it would circumvent the issues that past invasions kept running into. As for busting hegemonies, that I will admit is a wild suggestion but I think it could be worth a try. The trend of this game is for realms to grow big, very big, but for the overall number of realms to decrease, and this invasion mechanic could be a way of intermittently resetting this trend.