My top piece of feedback is considering some form of a strict mode, where your vision is not best effort support support for some legacy tool for a language, but fabulously amazing knock your socks off good support for users who take the time to invest in making their build friendly with your search index.
It might seem tempting to go after the longest common denominator audience here, but personally I think it's far more valuable to show users how code search can be amazing if they do their part to invest in it, vs. code search being "kind of sort of useful" if you have a fallback.
And maybe my Xoogler experiences are showing here, though Bazel / Kythe are in my opinion the perfect vehicles to realize that vision.