One of the design goals for K19 is the removal of all vendor proprietary interfaces. iMX6 is already gone and VDPAU/amcodec can be removed once the K18 release branch is forked. VAAPI gets a pass because it's no longer Intel specific (AMD and Allwinner will use it). One of the related design goals for LE10 is the removal of X11 and it's many dependencies.
The next generation Kodi video pipeline based on DRM/GBM allows us to support 10+ different GPU/SoC types (everything except nVidia) under a single framework and code path. There is nothing to stop someone implementing EGL streams, but it's not going to be popular with the main Kodi architects (given the design goals) and so far nobody is volunteering to do the work.
Unless that situation changes there will be a technical decision to terminate nVidia support after LE 9.0, and we are actively collecting stats on the number of installed devices with nVidia GPU's to quantify the impact of that decision. NB: If LE ends nVidia support you can still install drivers under Ubuntu or some other distro using Wayland or Xorg.
I'm one of those Nvidia users ATM. Can we take what you wrote to the bank? About "everything except nVidia" being supported? If that's the case, from what I understand an AMD RX560 should be supported and provide 10bit H265 in addition to 4k60 and HDR.
If that is the case I would not have a problem moving to AMD for the LE HTPC.