To create a faithful successor to 8th edition would require that either:
a) GW decides that destroying Warhammer was a mistake, and that it actually has plenty of value as the game it was.
or
b) GW decides that Warhammer was a solid foundation for a game, and with some fine-tuning to their approach, it can be as profitable for them as they'd like it to be.
I think (a) is unlikely. Though destroying Warhammer was a mistake in a moral and cultural sense, I think they did so because they became a company that existed to make money, rather than games, and Warhammer was not a recipe for making money. So I think the best-case scenario for The Old World is that they apply some of the things they've learned from AOS and other games, and adapt those things to make Warhammer conceptually faithful, while making it more flexible and profitable.
In particular, I think the idea of releasing models with their rules on an ongoing basis, rather than putting everything into a rulebook and running with it for years, is a concept that allows for both novelty-driven sales, as well as a way to balance armies on the fly, without having to rework the whole book. Warhammer could really benefit from that kind of piecemeal, more modular approach if done well.
Unfortunately, there are also other ways this can go that don't result in a faithful successor:
c) GW realizes that nostalgia can still be milked, and puts in the minimum effort so that The Old World 'looks' like Warhammer, without the depth.
d) GW realizes that Herohammer is more profitable than a proper war game, and goes all-in on that.
e) GW pulls another End Times, taking our favorite characters, peoples and places and ruining them all.
