I'm a heavy Go and Python user, and you're right that Go isn't particularly interesting--it doesn't change terribly rapidly, but it's also simple enough that you can do interesting and useful deep-dive sessions into the garbage collector or scheduler or other aspects of the runtime or the toolchain. You could also speculate or discuss proposals for Go2. There have also been significant recent changes to the dependency management scheme which affect pretty much everyone.

I don't think there's much of an analog for C. Most of the interesting stuff in C revolves around things you would think you can depend on but actually break in really weird and interesting ways (misc undefined behavior, sizes for integral types on different architectures, idiosyncracies of the preprocessor, the way to trivially exploit that pattern you used to avoid buffer overflow exploits). But most of that is just depressing.

I guess, some languages have to fight for their place under the sun, some don't.

That for different reasons. Go is not a general purpose language (it's creators specifically focus it's uses on networked apps). PHP is on the decline, nothing kills excitement like decline.