Some NVIDIA engineers probably know a lot about graphics stacks; charitably I'd say that those ones aren't the ones tasked with insisting on EGLStreams, which lacks a considerable number of crucial features.
To be honest though, NVIDIA engineers do not spend any time engineering graphics stacks at all; they write graphics drivers for stacks that are already largely specified. They're really good at shipping hundreds of megabytes of dirty hack code to patch popular shaders from ISVs to run slightly faster on their hardware, and probably great at writing shader compilers and threaded GL drivers.
Note the first comment there shows that their EGLStreams implementation shipped with vsync broken. EGLStreams seems attractive to NVIDIA because it was easy to implement (incorrectly). The features they talk about enabling on Tegra are not impossible with GBM, it just may involve adding a feature.
To be honest though, NVIDIA engineers do not spend any time engineering graphics stacks at all; they write graphics drivers for stacks that are already largely specified. They're really good at shipping hundreds of megabytes of dirty hack code to patch popular shaders from ISVs to run slightly faster on their hardware, and probably great at writing shader compilers and threaded GL drivers.