Personally I think all OpenMW-CS new features and almost all fixes can be covered in a single video. As for the engine itself, obviously shadows and recastnavigation should be demonstrated, a bunch of modding gimmicks additions too. Some of more significant changes easy to show in a video IMO are:
#4544 + #4805: they make the timing and the feeling of the Morrowind Prison Ship opening much closer to vanilla
#5004, #4961, maybe #5074 and #4787 and very maybe #5155 (you can lock actors too): for humorous moments. 4961 might be difficult to show in a video, but it can still be mentioned.
#4952: light source flickering was adjusted before, but it shouldn't need to be adjusted anymore.
#3006 + #4778: fixes for these make Interiors of Illusion puzzle in Sotha Sil Expanded mod solvable. SSE was mentioned before in a newspost, and this is the most obvious result of the compatibility improvement. You're supposed to hit a fire atronach with a projectile from the spell you get to light up the semitransparent road to your goal.
#4240 + #4783 + #4240: while there's still the problem with clouds during transition, ash storms and blizzards are much more sensible than before.
#4810: Rakis from Tamriel Rebuilt are very cute, and now they can move properly.
#4918 + #4989: both are necessary for the end-game Dagoth Ur to have his shield ability's VFX display properly. #4828 could be mentioned too.
#5122, #5147, #4962, #4540: Easy to show.
Aside from NiSwitchNode which basically shares its place with Glow in the Dahrk-like and Graphic Herbalism-like behavior demonstration NiRollController is a NIF record with the most obvious effect (rotation).
Of course not all of these must 100% be in a video.
And significant distant terrain optimizations should be mentioned.
Pedantry: these NIF record types aren't from the later format versions, they're still a part of 220.127.116.11 and are used in Morrowind mods. NIFs from later games can't yet be loaded in git revisions of openmw, although some very simple non-animated geometry from Oblivion and Civ4 can be in my branch. Overall it's obviously totally inferior to cc9cii's (not yet public) work. I had some positive response to an idea to explore some basic differences of the NIF format used in Morrowind versus the NIF format used in Oblivion in something intended to be published as a blog post. Maybe I'll get to writing that soon™.This allows for further work to support newer NIF features such as... NiRollController, NiSwitchNode, NiPalette, NiTriStrips and the fact that many NIFs from those later games can already be loaded into OpenMW.
There were cynic observations elsewhere that we mentioned Fallout 3 mesh loading but had no trace of Lua scripting in the recent newspost. Welp, the former is easier to add.