Merging architectures based on "time into the future" can sound appealing on paper, but often degenerates into really difficult sub-problems that end up making the whole thing less than ideal.
For example, in your suggested scenario, what happens if I find the utility of an already-formulated plan to be zero? What happens if I plan to do something but ignore its utility? Obviously that's not going to fly, so we have to compromise and integrate utility into the planning heuristics somehow. But now we need to know the utility of future hypothetical gamestates, so all we've really done is complicate both algorithms substantially. The handoff between the two designs is not clear or well defined, meaning that it will be hard to keep the two from polluting each other.
This is of course just an off-the-cuff example. When you get into the weeds of blending architectures, it often turns nasty because of this kind of thing. It is actually pretty hard to find disparate architectures that "hand off" well between them in the general case, when you're talking about time into the future blending. If you're lucky and your particular case doesn't have those thorny edges, cool; but otherwise you end up just writing a lot of special case hacks and workarounds that don't really suit the goal of getting the game done.
Layered architectures are a different thing. That's where you have a system that controls the fine-grained details and one or more additional systems that control the big picture stuff. They are designed to feed data back and forth, and to cooperate. Layering is a good thing and used all the time for things like strategy-vs-tactics distinctions, for example.
Occasionally there are architectures that work well across the "time into the future" spectrum. For example, utility architectures can be set up to do partial planning with some careful forethought. When you have a single solution for a wide range of problems, it's much more appealing to use that solution generally than to try and wire together a bunch of special cases.