I don't know a lot about this setting, so I might be very off-base, but I think the reason WotC isn't going to revive it has very little to do with the lore content being too whatever or not enough whatever. It could be a setting filled with proficiency bonus worshiping Ardlings (or whatever you imagine their secret dream setting is), and I think it would still be a no go, because the fundamental premise requires a substantial new rules subsystem. WotC really doesn't seem to like adding additional rules systems to the game (at least not ones with any meaningful complexity), and domain level management requires a substantial new rules subsystem. It also begs for a solid approach to mass combat, something 5e has yet to crack. It also just seems like a premise more at home in an era when player characters were expected to attract followers and establish strongholds, which is really not baked in to 5e D&D. And if players are doing things on a month by month scale, we probably need more robust handling of downtime as well.
Current 5e also generally struggles with shifting to a different scale of play, either in terms of combat scale, time scale, or zooming out to a management game. I don't know that this is necessary a rules limitation per se, so much as an issue of 5e players being so rarely asked to do something on a different scale that way that it is jarring and weird to shift to using their characters in a different way. 5e D&D is conceptually a system where you always have the same abilities, and even when you are out of initiative your character's life consists of 10 turns per minute, each with action, bonus action, and reaction. Shifting into different subsystems where you have different abilities is not something WotC is particularly interested in.
Which all sounds like reasons to me why someone could do a really cool Birthright-inspired supplement, or a 5e clone reworking the system from the ground up to support that sort of play, with applicable abilities baked deep into the classes and such (which I think is what I would need as a 5e player, for it to really be a satisfying experience). But WotC won't be the ones to do it.