To be fair, GNU/Linux distros like Debian lean very heavily on the GNU part. They owe a lot to the GSF and its work is highly praised.
Just their kernel somehow seems to be stuck in vaporware status. Probably because a lot of developers would think "why work on this when we already have Linux" which is a fair point too.
I wonder if microkernels more relevant now than ever given their reduced attack surface, and also the recent availability of more cores.
One big criticism from decades ago was the loss in efficiency. But what's changed since microkernels were conceived is how many processor cores are available to offload userspace drivers from the kernel.
Is this a valid viewpoint? Is it time for microkernels to overtake monolithic kernels?
They already did. There are more microkernels around than monolithic. All big CPU's use them internally, all phones use them.