It'll just have different design decisions and flaws. Expecting anything else is unrealistic. Bit-rot means that X isn't as well-suited to today's environment as we'd like, but I'm sure that some things in X that are regarded as mistakes now were trumpeted as great advancements when they were introduced. Similarly, Wayland will someday be in the same position.

That doesn't mean that it's not a net-positive to develop and start using it, of course.