I suppose they might use NVM to interface with Nintendo specific hardware, they don't need it for graphics. So if engine developers are smart, they minimize NVM usage to only those corner cases, since there is no need to reinvent the wheel and duplicate work.
>yet is used as much as GL ES 1.0 was on the PS3.
Any Vulkan based engine can use it. Wasn't there Doom release for Switch?
Most Switch games are done in Unity, Unreal, Crysis and a couple of other lesser known middleware engines, taking advantage of NVN.