I'm the tech lead for a startup with just a handful of programmers. I'm interested in hiring someone who can help us come up with well-architected, novel solutions to the problems that we're already solving. The issue is, we're solving them in a way that turns out to be pretty difficult to maintain and change. I'd like a totally new, fresh approach that takes the lessons we've learned and creates something that's much easier to write fixes for, much easier to extend with new features.
I need someone who doesn't just build on top of existing, well-defined codebases/APIs. I need someone who has the ability to engineer a complete, well-rounded, extensible codebase/API himself.
It would seem to be remarkably difficult to test for this ability. Even work samples that can be done in the short time period you describe wouldn't be able to test for this ability.