From what I can tell from the help center, questions that are about such a high-level review are not considered in the scope. How about answers that address such points, even though they weren't put up for consideration?
Reviewers are always free to voice concerns about any & all aspects of the code - and since the code is the design, the design is always somewhat implicitly up for review as well.
We ask that reviewees post their actual implementation, because "any & all aspects of the code" includes more than just the high-level design, so an asker posting a hypothetical implementation that's really just presenting a design, in such a way that really only the design is up for review, would be off-topic.
However if a reviewee posts their completed design (through their working code) and you come along and see design flaws, just like if a reviewer comes along and sees a bug that the OP missed, then that's when OP possibly gets the most out of CR!
TL;DR: These restrictions are for questions, to make sure the code posted is in a reviewable state - answers don't have these restrictions.