Note that this is formal verification of an imperative, C-based program manipulating low-level structures done years ago. I wouldnt say that represents what we're currently capable of in general case. For starters, a functional program or imperative without pointers (eg in SPARK) is much easier to verify than a C program. Plus, the seL4 organization recently reduced effort for filesystems down by a few multiples with a functional language.

Truth is the seL4 team set themselves up for a harder-than-usual job. For good reason but most folks (esp managed languages) won't see as much difficulty.