It’s not fully open source yet (ie you can’t use it yourself I think) but Facebook’s EdenFS project solves the partial checkout problem.

The queries in Bazel/Buck to figure out the changed set of dependencies probably isn’t complicated and that’s why there’s no turnkey solution? You do need to adopt a build system with precise dependency tracking (afaik only Buck and Bazel support that) or the monorepo path isn’t going to be very successful.