For what it is worth, GCs are a major headache generally for system level code. The expense in terms of system behavior are far higher than the implied CPU time due to the scheduling issues. This has always been the challenge of GC-centric environments.

I think there are two big challenges for garbage collected environments with respect to core server systems level code. First, an acceptable pause needs to be reliably sub-millisecond or it breaks the userspace schedulers in a lot of high-performance server code. In the video presentation, they had a difficult time guaranteeing 10 milliseconds. They are working on it but this is a problem. Second, most high-performance server engines eliminate almost everything that looks like context-switching, mostly because it is very expensive on modern hardware. The idea that there may be hundreds or even thousands of threads running on real servers does not comport with the reality of a lot of server environments where context switching is severely restricted for good reason. The idea that it makes sense to have a lot of background processes cleaning up the memory allocation contradicts many well-conceived software architectures. These days, everything is explicitly scheduled and bounded if server performance matters.