The use cases (specifically macros) might be rather complex to solve that - having explicit declarations of the read and initialization make solving that logically easier. I could imagine that if the solver could apply that (which I'm not sure it is generally solvable) that type of enhancement could be added later.
In the mean time attached macros would gain considerably easier use at minimal cost (since they have the proper information for synthesis).
Overall the pitch looks fantastic; I really think the struct Angle is a compelling example. For a use case Observation is a prime candidate; it will make initialization feel natural.