Tooling should get us part of the way - it surely cannot be that difficult to interactively show which interfaces a type satisfies (and conversely, what you'd need to add to a type to have it satisfy an interface).

In general it would be neat if the "go" command supported some more advanced static analysis stuff beyond go fix, fmt, and vet.

A lot of this stuff could be done by reflect -- if only there was a repl!