In the previous post, I discussed how in canon Midnight, it is essential for players to exploit the divisive nature of the powers of darkness in order to win breathing room to perform acts of good. An alternative solution, however, is to replace the monolithic Izrador with a pantheon of dark deities, or even demon lords (one inspiration for this post is Courtney's post on the demon-nature some week or two ago), each with its own agents, champions, church, realm, and armies. This gives us something more like Warhammer's cosmology of evil, or Dark Sun's dragon-kings. This ideological and temporal variety means that players are more likely to find evil powers who are acceptable to their sensibilities (the better to tempt them), and would give a DM more leeway in functioning economies and easier-to-work-with legal structures. On the flip side, part of the reason Midnight works is that it is a darkened mirror of Tolkein, from which many of D&D's tropes springeth. By splitting Izsauradoron into many competing facets, we make this resemblance less recognizable, and I suspect the setting would lose some of its lustre as a result. Depending on how the world arrived at an evil-dominant cosmology, we might also lose that one glimmer of distant hope in Midnight, that the Old Gods are still waiting outside the Veil.
So I'm not convinced this is a particularly ideal course for Midnight proper, but a "Demon Realms" game combining Midnight, Dark Sun, and Raveloft might be fun in its own right.